[FIR2IR] Manage script symbols in declaration storage instead of declaration generator

This is needed to be able to implement creation of unbound symbols
  for references of corresponding declarations (KT-62856)

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/Fir2IrDeclarationStorage.kt

@@ -1129,11 +1129,19 @@ class Fir2IrDeclarationStorage(
 
     fun getOrCreateIrScript(script: FirScript): IrScript {
         getCachedIrScript(script)?.let { return it }
-        return callablesGenerator.createIrScript(script).also {
+        val symbol = createScriptSymbol(signatureComposer.composeSignature(script))
+        return callablesGenerator.createIrScript(script, symbol).also {
             scriptCache[script] = it
         }
     }
 
+    private fun createScriptSymbol(signature: IdSignature?): IrScriptSymbol {
+        return when {
+            signature != null -> symbolTable.referenceScript(signature)
+            else -> IrScriptSymbolImpl()
+        }
+    }
+
     // ------------------------------------ scoping ------------------------------------
 
     fun enterScope(symbol: IrSymbol) {

compiler/fir/fir2ir/src/org/jetbrains/kotlin/fir/backend/generators/Fir2IrCallableDeclarationsGenerator.kt

@@ -928,16 +928,13 @@ class Fir2IrCallableDeclarationsGenerator(val components: Fir2IrComponents) : Fi
 
     // ------------------------------------ scripts ------------------------------------
 
-    fun createIrScript(script: FirScript): IrScript = script.convertWithOffsets { startOffset, endOffset ->
-        val signature = signatureComposer.composeSignature(script)!!
-        symbolTable.declareScript(signature, { IrScriptPublicSymbolImpl(signature) }) { symbol ->
-            IrScriptImpl(symbol, script.name, irFactory, startOffset, endOffset).also { irScript ->
-                irScript.origin = SCRIPT_K2_ORIGIN
-                irScript.metadata = FirMetadataSource.Script(script)
-                irScript.implicitReceiversParameters = emptyList()
-                irScript.providedProperties = emptyList()
-                irScript.providedPropertiesParameters = emptyList()
-            }
+    fun createIrScript(script: FirScript, symbol: IrScriptSymbol): IrScript = script.convertWithOffsets { startOffset, endOffset ->
+        IrScriptImpl(symbol, script.name, irFactory, startOffset, endOffset).also { irScript ->
+            irScript.origin = SCRIPT_K2_ORIGIN
+            irScript.metadata = FirMetadataSource.Script(script)
+            irScript.implicitReceiversParameters = emptyList()
+            irScript.providedProperties = emptyList()
+            irScript.providedPropertiesParameters = emptyList()
         }
     }
 

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/util/SymbolTable.kt

@@ -59,6 +59,10 @@ open class SymbolTable(
         )
     }
 
+    fun referenceScript(signature: IdSignature): IrScriptSymbol {
+        return scriptSlice.referenced(signature) { IrScriptPublicSymbolImpl(signature) }
+    }
+
     // ------------------------------------ class ------------------------------------
 
     fun declareClass(