Add fat jars for gradle plugin (#2149)

* [gradle-plugin] Bundle big Kotlin plugin into the native plugin jar

* Use big Kotlin's version in the Gradle plugin

* [gradle-plugin] Exclude big Kotlin plugins from final jar

* Use composite build again

* Remove MULTIPLATFORM.md

* [gradle-plugin] Fix adding common sources

* [gradle-plugin] Fix test running

build.gradle

@@ -167,7 +167,7 @@ task gradlePluginJar {
     dependsOn gradle.includedBuild('kotlin-native-gradle-plugin').task(':shadowJar')
 }
 
-task gradlePluginCheck() {
+task gradlePluginCheck {
     dependsOn gradle.includedBuild('kotlin-native-gradle-plugin').task(':check')
 }