refactor(docs): update the contributing docs (scala#17585)

This makes a bunch of small updates the contributing docs that were
recently migrated over from the scala-lang site. I think there are
actually some more updates to be done, but much of these changes are
just structural. To sort of summarize this does the following:

- gets rid of old irrelevant things like the `checklist.sh`
- removes some instructions that are no longer relevant
- re-organizes the side bar to better group things by topic
- gets rid of redundant information and tries to group things better
- moves the scaladoc docs into the contributing docs

I'll add some more comments inline to further explain.

[skip community_build]

_Old sidebar_

<img width="321" alt="Screenshot 2023-05-25 at 15 18 32"
src="https://github.com/lampepfl/dotty/assets/13974112/2e493110-8098-445c-b101-166998c7c95f">

_New sidebar_
<img width="321" alt="Screenshot 2023-05-25 at 15 18 03"
src="https://github.com/lampepfl/dotty/assets/13974112/2f86764e-bc3e-4356-9f56-006197a10153">

docs/_docs/contributing/cheatsheet.md

@@ -0,0 +1,37 @@
+---
+layout: doc-page
+title: Command Cheatsheet
+---
+
+## sbt commands
+
+Below is a cheat sheet of some frequently used commands to be used from SBT
+console – `sbt`.
+
+
+|                        Command                       |                                                          Description                                                          |
+|------------------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------|
+| `scala3/scalac`                                      | Run the compiler directly, with any current changes.                                                                          |
+| `scala3/scala`                                       | Run the main method of a given class name.                                                                                    |
+| `scalac ../issues/Playground.scala`                  | Compile the given file – path relative to the Dotty directory. Output the compiled class files to the Dotty directory itself. |
+| `scala Playground`                                   | Run the compiled class `Playground`. Dotty directory is on classpath by default.                                              |
+| `repl`                                               | Start REPL                                                                                                                    |
+| `scala3/scalac -print-tasty Foo.tasty`               | Print the TASTy of top-level class `Foo`                                                                                      |
+| `scala3-bootstrapped/test`                           | Run all tests for Scala 3. (Slow, recommended for CI only)                                                                    |
+| `scala3-bootstrapped/publishLocal`                   | Build Scala 3 locally. (Use to debug a specific project)                                                                      |
+| `testOnly dotty.tools.dotc.CompilationTests -- *pos` | Run test (method) `pos` from `CompilationTests` suite.                                                                        |
+| `testCompilation sample`                             | In all test suites, run test files containing the word `sample` in their title.                                               |
+| `scala3-compiler/Test/runMain dotty.tools.printTypes`| Print types underlying representation                                                                                         |
+| `scaladoc/generateScalaDocumentation`                | Build the documentation website (published to https://dotty.epfl.ch)                                                          |
+| `scaladoc/generateReferenceDocumentation`            | Build the reference documentation website (published to https://docs.scala-lang.org/scala3/reference)                         |
+
+
+## Shell Commands
+
+Below is a cheat sheet of some frequently used commands to be used from your
+shell.
+
+| Command                              | Description                                                      |
+|--------------------------------------|------------------------------------------------------------------|
+| `rm -rv *.tasty *.class out || true` | clean all compiled artifacts, from root dotty directory          |
+| `git clean -fdx`                     | a full clean of all files in the codebase not tracked by git     |

docs/_docs/contributing/debugging/debugging.md

@@ -0,0 +1,14 @@
+---
+layout: doc-page
+title: Debugging the Compiler
+redirectFrom: /docs/contributing/issues/debugging.html
+---
+
+This section goes over the various ways to debug either the compiler or the code
+that you're having issues with. This can be just inspecting the trees of your
+code or stepping through the dotty codebase with a Debugger.
+
+The following sections will help you with this:
+- [Debugging with your IDE](./ide-debugging.md.md)
+- [How to Inspect Values](./inspection.md)
+- [Other Debugging Techniques](./other-debugging.md)

docs/_docs/contributing/issues/debugging.md → docs/_docs/contributing/debugging/ide-debugging.md

@@ -1,6 +1,6 @@
 ---
 layout: doc-page
-title: Debugging the Compiler
+title: Debugging with your IDE
 ---
 
 The debugger is a powerful tool to navigate the internals of the compiler and track bugs.

docs/_docs/contributing/issues/inspection.md → docs/_docs/contributing/debugging/inspection.md

@@ -1,6 +1,7 @@
 ---
 layout: doc-page
 title: How to Inspect Values
+redirectFrom: /docs/contributing/issues/inspection.html
 ---
 
 In this section, you will find out how to debug the contents of certain objects
@@ -11,7 +12,10 @@ while the compiler is running, and inspect produced artifacts of the compiler.
 Frequently you will need to inspect the content of a particular variable.
 You can either use `println`s or the debugger, more info on how to setup the latter.
 
-In the remeainder of this article we'll use `println(<someUsefulExpression>)` inserted in the code, but the same effect can be accomplished by stopping at a breakpoint, and typing `<someUsefulExpression>` in the [debug console](./debugging.md#the-debug-console) of the debugger.
+In the remainder of this article we'll use `println(<someUsefulExpression>)`
+inserted in the code, but the same effect can be accomplished by stopping at a
+breakpoint, and typing `<someUsefulExpression>` in the [debug
+console](./ide-debugging.md#the-debug-console) of the debugger.
 
 When printing a variable, it's always a good idea to call `show` on that variable: `println(x.show)`.
 Many objects of the compiler define `show`, returning a human-readable string.
@@ -102,6 +106,7 @@ If you are curious about the representation of a type, say `[T] =>> List[T]`,
 you can use a helper program [dotty.tools.printTypes][DottyTypeStealer],
 it prints the internal representation of types, along with their class. It can be
 invoked from the sbt shell with three arguments as follows:
+
 ```bash
 sbt:scala3> scala3-compiler/Test/runMain
   dotty.tools.printTypes