[Platform API] Split TargetPlatform into lightweight TargetPlatform and CompilerServices

This decouples simple data (TargetPlatform) from other subsystem-specific
logic (like default imports, built-ins, etc.).

Aside from purely aesthetic improvements, it also makes it easier
to move 'TargetPlatform' into core (see next commits)

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/scopes/impl/FirDefaultSimpleImportingScope.kt

@@ -18,7 +18,7 @@ class FirDefaultSimpleImportingScope(session: FirSession) : FirAbstractSimpleImp
 
     override val simpleImports = run {
         val importResolveTransformer = FirImportResolveTransformer(session)
-        session.moduleInfo?.platform?.getDefaultImports(LanguageVersionSettingsImpl.DEFAULT, true)
+        session.moduleInfo?.compilerServices?.getDefaultImports(LanguageVersionSettingsImpl.DEFAULT, true)
             ?.filter { !it.isAllUnder }
             ?.map {
                 FirImportImpl(session, null, it.fqName, isAllUnder = false, aliasName = null)

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/scopes/impl/FirDefaultStarImportingScope.kt

@@ -14,7 +14,7 @@ class FirDefaultStarImportingScope(session: FirSession, lookupInFir: Boolean = f
     FirAbstractStarImportingScope(session, lookupInFir) {
 
     // TODO: put languageVersionSettings into FirSession?
-    override val starImports = session.moduleInfo?.platform?.getDefaultImports(LanguageVersionSettingsImpl.DEFAULT, true)
+    override val starImports = session.moduleInfo?.compilerServices?.getDefaultImports(LanguageVersionSettingsImpl.DEFAULT, true)
         ?.filter { it.isAllUnder }
         ?.map {
             FirResolvedImportImpl(

compiler/fir/resolve/tests/org/jetbrains/kotlin/fir/AbstractFirDiagnosticsSmokeTest.kt

@@ -23,8 +23,10 @@ import org.jetbrains.kotlin.fir.resolve.impl.FirProviderImpl
 import org.jetbrains.kotlin.fir.resolve.transformers.FirTotalResolveTransformer
 import org.jetbrains.kotlin.name.Name
 import org.jetbrains.kotlin.resolve.MultiTargetPlatform
+import org.jetbrains.kotlin.resolve.PlatformDependentCompilerServices
 import org.jetbrains.kotlin.resolve.TargetPlatform
 import org.jetbrains.kotlin.resolve.jvm.platform.JvmPlatform
+import org.jetbrains.kotlin.resolve.jvm.platform.JvmPlatformCompilerServices
 import java.io.File
 import java.util.*
 
@@ -144,6 +146,9 @@ abstract class AbstractFirDiagnosticsSmokeTest : BaseDiagnosticsTest() {
         override val platform: TargetPlatform?
             get() = JvmPlatform
 
+        override val compilerServices: PlatformDependentCompilerServices
+            get() = JvmPlatformCompilerServices
+
         override fun dependencies(): List<ModuleInfo> {
             return listOf(this)
         }
@@ -153,6 +158,9 @@ abstract class AbstractFirDiagnosticsSmokeTest : BaseDiagnosticsTest() {
         override val platform: TargetPlatform?
             get() = JvmPlatform
 
+        override val compilerServices: PlatformDependentCompilerServices
+            get() = JvmPlatformCompilerServices
+
         val dependencies = mutableListOf<ModuleInfo>(this)
         override fun dependencies(): List<ModuleInfo> {
             return dependencies