[K/N][build] Composite build with build.tools-conventions plugin

Adds convention plugin instead of sources inclusion
inside the buildSrc, effectively reducing the amount
of the code to be compiled in buildSrc.

Merge-request: KT-MR-8898

kotlin-native/build.gradle

@@ -50,6 +50,8 @@ if (isMac()) {
     checkXcodeVersion(project)
 }
 
+apply plugin: "kotlin.native.build-tools-conventions"
+
 ext {
     distDir = UtilsKt.getKotlinNativeDist(project)
     dependenciesDir = DependencyProcessor.defaultDependenciesRoot