KopyKat Gradle plugin

[aSemy]

Here's an initial attempt. It's still a little rough, but it's ready for a first look.

fixes #29

It requires some setup:

1. use a JitPack workaround to allow for JitPack to host Gradle Plugins

   // $projectRootDir/settings.gradle.kts
   pluginManagement {
      repositories {
          gradlePluginPortal()
          maven("https://jitpack.io")
      }
      resolutionStrategy {
          eachPlugin {
              if (requested.id.id == "at.kopykat") {
                  // TODO change to kopykat repo
                  useModule("com.github.aSemy.kopykat:kopykat-gradle-plugin:${requested.version}")
              }
          }
      }
   }

2. import the plugin

   // build.gradle.kts
   
   plugins {
     id("at.kopykat") version "feat~gradle_plugin-SNAPSHOT"
     id("com.google.devtools.ksp") version "1.7.10-1.0.6" // TODO why isn't KSP plugin applied automatically by kopykat plugin?
   }
   
   kopykat {
    copyMap.set(true)
   }
   
   dependencies {
      ksp("com.github.kopykat-kt.kopykat:ksp:1.0-rc1") // TODO kopykat should add this automatically
   }

Notes:

• To keep this PR small I haven't implemented tests https://docs.gradle.org/current/userguide/testing_gradle_plugins.html

[serras]

I think we should be careful with this, and ensure that it doesn’t get harder than the current instructions. My experience with this is that a custom plug-in sometimes fail on Android or MPP, for which KSP has special instructions.

[aSemy]

Yeah, the plugin instructions would be easier if the KopyKat plugin can be published to Maven Central or the Gradle Plugin Portal. JitPack manually overrides the project's group, which in turn breaks the Gradle plugin marker. If published on Maven Central, the resolutionStrategy {} workaround isn't needed.

The plugin in this PR shouldn't cause problems with Kotlin Multiplatform, but users might have to manually enable KSP per source set. There's ways to test for this though, either manually with example projects, or with Gradle TestKit. I can include them in this PR, if you'd like? But I think that would make it too large.

Can you find the special instructions for Android? I could only find them for Kotlin Multiplatform.

[serras]

I'm working on publishing to Maven Central (#41), which should make things easier