Add detekt compiler plugin to main project

[3flex]

This brings the detekt compiler plugin into the primary project. Aside from bringing the code over, this also makes changes to the Gradle plugin so that the standard plugin as well as the compiler plugin can be used in the same project. This wasn't previously possible due to the naming conflict on the detekt extension which was applied by both Gradle plugins.

I'd like to get this merged, then we can work on:

• Confirming the versioning scheme for the compiler plugin which will be sensitive to the Kotlin version the target project is using. I propose just copying KSP's version scheme of $kotlinVersion-$pluginVersion e.g. 1.7.20-1.22.0-RC2
• Docs
• Pushing out at least one release (can then skip step 1 below)
• Work on a fix for InvalidPackageDeclaration failures (means we can skip steps 3 & 4 below)

To test:

1. Include these builds in the test project's settings.gradle(.kts) file:

includeBuild("../detekt/detekt-gradle-plugin")
includeBuild("../detekt")

2. Apply the compiler plugin in a target project:

plugins {
    id("io.github.detekt.gradle.compiler-plugin")
}

3. Add a detekt.yml config file and disable InvalidPackageDeclaration (see detekt-compiler-plugin/issues/15):

naming:
  InvalidPackageDeclaration:
    active: false

4. Set buildUponDefaultConfig = true, e.g.:

detekt {
    buildUponDefaultConfig = true
}

The compiler plugin cannot be applied to the detekt project itself due to circular dependencies, which I couldn't work around, but hope to some time in future.

Closes #3520

[github-advanced-security]

detekt found more than 10 potential problems in the proposed changes. Check the Files changed tab for more details.

[codecov]

Codecov Report

Merging #5492 (f2690cf) into main (342c228) will increase coverage by 85.89%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##             main    #5492       +/-   ##
===========================================
+ Coverage        0   85.89%   +85.89%     
- Complexity      0     3637     +3637     
===========================================
  Files           0      516      +516     
  Lines           0    12179    +12179     
  Branches        0     2171     +2171     
===========================================
+ Hits            0    10461    +10461     
- Misses          0      628      +628     
- Partials        0     1090     +1090     

Impacted Files	Coverage Δ
.../arturbosch/detekt/rules/style/CanBeNonNullable.kt	73.20% <0.00%> (ø)
...ekt/rules/style/RedundantVisibilityModifierRule.kt	98.24% <0.00%> (ø)
...rturbosch/detekt/rules/style/OptionalWhenBraces.kt	94.11% <0.00%> (ø)
...b/arturbosch/detekt/rules/complexity/LargeClass.kt	94.87% <0.00%> (ø)
.../detekt/metrics/processors/KtFileCountProcessor.kt	100.00% <0.00%> (ø)
...t/rules/coroutines/SuspendFunWithFlowReturnType.kt	83.33% <0.00%> (ø)
...bosch/detekt/rules/naming/BooleanPropertyNaming.kt	94.28% <0.00%> (ø)
...detekt/metrics/processors/PackageCountProcessor.kt	100.00% <0.00%> (ø)
.../arturbosch/detekt/core/baseline/BaselineFacade.kt	86.66% <0.00%> (ø)
...ormatting/wrappers/FunctionTypeReferenceSpacing.kt	100.00% <0.00%> (ø)
... and 506 more

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[schalkms]

First of all, big shoutout to you @3flex! Great stuff 👍

I'd like to get this merged

I understand, that we are confident enough that the standard and compiler plugin can coexist for upcoming versions, without interfering each other. If so, I'm very pleased with merging this.

• Confirming the versioning scheme for the compiler plugin which will be sensitive to the Kotlin version the target project is using. I propose just copying KSP's version scheme of $kotlinVersion-$pluginVersion e.g. 1.7.20-1.22.0-RC2

Agreed.

• Docs

I think the focus should be on the restrictions for the compiler plugin. Maybe, the readme from the compiler plugin can be copied over to a separate detekt.dev webpage.

[3flex]

I propose to add docs in a separate PR. I'll open an issue for tracking once this is merged.