Add code lens for running tests

[vinistock]

Discover test examples using the code lens request and return Run entries for each one plus one for running the entire file at the class level.

We should

• Support only Minitest / test-unit for now
• Allow running specific examples or the entire test class
• Use the data attribute (which allows for any information we want) to
  • Specify that the code lens is a test (e.g.: type: "test"). This will make it easier to create a test controller on VS Code
  • Specify the command that the client should use to execute that test. It'll most likely be TESTOPTS="-n='/NAME_OF_THE_TEST/'" ruby -Itest PATH_TO_TEST_FILE. Do not use rake since we want to be able to run tests even in projects that may not be using it

Note: this also involves creating a VS Code command that is used to execute the test. The first version of this should only grab whatever command was received in the data attribute and run that in the terminal.

Documentation: https://microsoft.github.io/language-server-protocol/specification#textDocument_codeLens

[matteeyah]

This is related to https://github.com/connorshea/vscode-ruby-test-adapter

Since this conflicts with the functionality of that plugin, it'd be cool if https://github.com/Shopify/vscode-ruby-lsp could be used as a drop in replacement.

The main things that I think are missing are starting a debugging session for a test (which could lean on https://github.com/ruby/vscode-rdbg) and showing all tests in the native VS Code test explorer (#1554).

[adisonlampert]

@matteeyah

The main things that I think are missing as of right is starting a debugging session for a test

This is one of our goals. We've been working on setting up ruby/debug (for example, #1542 & Shopify/vscode-ruby-lsp#539). Adding test running capability is just the first step 😃