K2: Introduce FirCachingCompositeSymbolProvider

The main idea is pre-computing the sets of names that might be
met there, that helps to decrease the sizes of the backing maps
(by avoiding irrelevant keys)

Totally, this branch with previous commits speeds up MT Full Kotlin
approximately on 3 seconds (~5%)

analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/providers/LLFirModuleWithDependenciesSymbolProvider.kt

@@ -77,6 +77,12 @@ internal class LLFirModuleWithDependenciesSymbolProvider(
         getPackageWithoutDependencies(fqName)
             ?: dependencyProvider.getPackage(fqName)
 
+    override fun computePackageSetWithTopLevelCallables(): Set<String>? = null
+
+    override fun knownTopLevelClassifiersInPackage(packageFqName: FqName): Set<String>? = null
+
+    override fun computeCallableNamesInPackage(packageFqName: FqName): Set<Name>? = null
+
 
     fun getPackageWithoutDependencies(fqName: FqName): FqName? =
         providers.firstNotNullOfOrNull { it.getPackage(fqName) }
@@ -150,6 +156,10 @@ internal abstract class LLFirDependentModuleProviders(
             }
         }
 
+    // TODO: Consider having proper implementations for sake of optimizations
+    override fun computePackageSetWithTopLevelCallables(): Set<String>? = null
+    override fun knownTopLevelClassifiersInPackage(packageFqName: FqName): Set<String>? = null
+    override fun computeCallableNamesInPackage(packageFqName: FqName): Set<Name>? = null
 
     private fun <S : FirCallableSymbol<*>> addNewSymbolsConsideringJvmFacades(
         destination: MutableList<S>,

analysis/low-level-api-fir/src/org/jetbrains/kotlin/analysis/low/level/api/fir/providers/LLFirProvider.kt

@@ -113,6 +113,11 @@ internal class LLFirProvider(
         override fun getPackage(fqName: FqName): FqName? =
             providerHelper.getPackage(fqName)
 
+        // TODO: Consider having proper implementations for sake of optimizations
+        override fun computePackageSetWithTopLevelCallables(): Set<String>? = null
+        override fun knownTopLevelClassifiersInPackage(packageFqName: FqName): Set<String>? = null
+        override fun computeCallableNamesInPackage(packageFqName: FqName): Set<Name>? = null
+
         override fun getClassLikeSymbolByClassId(classId: ClassId): FirClassLikeSymbol<*>? {
             return getFirClassifierByFqName(classId)?.symbol
         }