[AA] Add KtEnumEntryInitializerSymbol

- An enum entry's body is an initializer with members only accessible
  within that body. Because users of the Analysis API might want to
  analyze the members of the enum entry initializer, we expose this
  initializer via `KtEnumEntrySymbol`. The initializer only exists if
  the enum entry has a body.
  - We already have some usages of the initializer inside symbol light
    classes, which generate a light class for each enum entry, which
    includes the enum entry's hidden members.
- To hide the implementation detail that initializers are anonymous
  objects, `KtEnumEntryInitializerSymbol` is simply a
  `KtSymbolWithMembers`.
- The advantage of making it a `KtSymbolWithMembers`, instead of
  providing a custom way to get a member scope, is that we can pass
  around the initializer easily, e.g. in `KtEnumEntrySymbolRenderer`.
- We implement `KtEnumEntryInitializerSymbol` directly as a
  `KtFirAnonymousObjectSymbol` without a wrapper. This has a few
  advantages:
  1. We can directly benefit from the anonymous object symbol being a
     `KtSymbolWithMembers`, so we don't have to handle enum entry
     initializers specially in e.g. `KtFirScopeProvider`.
  2. We don't have to implement a new symbol restoration mechanism for
     the initializer.
  3. This implementation matches the actual FIR tree structure (with a
     simplification that the connecting anonymous object expression
     between the enum entry and the initializing anonymous object is
     omitted).

^KT-61425 fixed

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/symbols/KtFirAnonymousObjectSymbol.kt

@@ -16,6 +16,7 @@ import org.jetbrains.kotlin.analysis.api.fir.symbols.pointers.requireOwnerPointe
 import org.jetbrains.kotlin.analysis.api.fir.utils.cached
 import org.jetbrains.kotlin.analysis.api.lifetime.withValidityAssertion
 import org.jetbrains.kotlin.analysis.api.symbols.KtAnonymousObjectSymbol
+import org.jetbrains.kotlin.analysis.api.symbols.KtEnumEntryInitializerSymbol
 import org.jetbrains.kotlin.analysis.api.symbols.pointers.CanNotCreateSymbolPointerForLocalLibraryDeclarationException
 import org.jetbrains.kotlin.analysis.api.symbols.pointers.KtPsiBasedSymbolPointer
 import org.jetbrains.kotlin.analysis.api.symbols.pointers.KtSymbolPointer
@@ -25,7 +26,7 @@ import org.jetbrains.kotlin.fir.symbols.impl.FirAnonymousObjectSymbol
 internal class KtFirAnonymousObjectSymbol(
     override val firSymbol: FirAnonymousObjectSymbol,
     override val analysisSession: KtFirAnalysisSession,
-) : KtAnonymousObjectSymbol(), KtFirSymbol<FirAnonymousObjectSymbol> {
+) : KtAnonymousObjectSymbol(), KtEnumEntryInitializerSymbol, KtFirSymbol<FirAnonymousObjectSymbol> {
     override val psi: PsiElement? = withValidityAssertion { firSymbol.fir.getAllowedPsi() }
 
     override val annotationsList by cached {

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/symbols/KtFirEnumEntrySymbol.kt

@@ -15,11 +15,15 @@ import org.jetbrains.kotlin.analysis.api.fir.symbols.pointers.KtFirEnumEntrySymb
 import org.jetbrains.kotlin.analysis.api.fir.symbols.pointers.requireOwnerPointer
 import org.jetbrains.kotlin.analysis.api.fir.utils.cached
 import org.jetbrains.kotlin.analysis.api.lifetime.withValidityAssertion
+import org.jetbrains.kotlin.analysis.api.symbols.KtEnumEntryInitializerSymbol
 import org.jetbrains.kotlin.analysis.api.symbols.KtEnumEntrySymbol
 import org.jetbrains.kotlin.analysis.api.symbols.pointers.KtPsiBasedSymbolPointer
 import org.jetbrains.kotlin.analysis.api.symbols.pointers.KtSymbolPointer
 import org.jetbrains.kotlin.analysis.api.types.KtType
+import org.jetbrains.kotlin.fir.declarations.FirResolvePhase
+import org.jetbrains.kotlin.fir.expressions.FirAnonymousObjectExpression
 import org.jetbrains.kotlin.fir.symbols.impl.FirEnumEntrySymbol
+import org.jetbrains.kotlin.fir.symbols.lazyResolveToPhase
 import org.jetbrains.kotlin.name.CallableId
 import org.jetbrains.kotlin.name.ClassId
 import org.jetbrains.kotlin.name.Name
@@ -41,6 +45,20 @@ internal class KtFirEnumEntrySymbol(
 
     override val callableIdIfNonLocal: CallableId? get() = withValidityAssertion { firSymbol.getCallableIdIfNonLocal() }
 
+    override val enumEntryInitializer: KtEnumEntryInitializerSymbol? by cached {
+        if (firSymbol.fir.initializer == null) {
+            return@cached null
+        }
+
+        firSymbol.fir.lazyResolveToPhase(FirResolvePhase.BODY_RESOLVE)
+
+        val initializerExpression = firSymbol.fir.initializer
+        check(initializerExpression is FirAnonymousObjectExpression) {
+            "Unexpected enum entry initializer: ${initializerExpression?.javaClass}"
+        }
+        KtFirAnonymousObjectSymbol(initializerExpression.anonymousObject.symbol, analysisSession)
+    }
+
     context(KtAnalysisSession)
     override fun createPointer(): KtSymbolPointer<KtEnumEntrySymbol> = withValidityAssertion {
         KtPsiBasedSymbolPointer.createForSymbolFromSource(this) ?: KtFirEnumEntrySymbolPointer(requireOwnerPointer(), firSymbol.name)