[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

settings.gradle

@@ -788,6 +788,7 @@ project(':kotlin-scripting-ide-common').projectDir = "$rootDir/plugins/scripting
 // Uncomment to use locally built protobuf-relocated
 // includeBuild("dependencies/protobuf")
 if (buildProperties.isKotlinNativeEnabled) {
+    includeBuild("kotlin-native/build-tools")
     include ':kotlin-native:dependencies'
     include ':kotlin-native:endorsedLibraries:kotlinx.cli'
     include ':kotlin-native:endorsedLibraries'
@@ -810,7 +811,6 @@ if (buildProperties.isKotlinNativeEnabled) {
     include ':kotlin-native:backend.native:tests'
     include ":kotlin-native-compiler-embeddable"
     project(":kotlin-native-compiler-embeddable").projectDir = "$rootDir/kotlin-native/prepare/kotlin-native-embeddable-compiler" as File
-    include ':kotlin-native:build-tools'
     include ':kotlin-native-shared'
     project(":kotlin-native-shared").projectDir = "$rootDir/kotlin-native/shared" as File
 }