[FIR] FirScriptConfigurationExtensionImpl: change source element for result$$ property

We should use the source from replaced `FirAnonymousInitializer` as it
is more equivalent. Another point – the previous implementation
duplicated the source between generated FirProperty and initializer

^KT-65344

analysis/low-level-api-fir/testData/getOrBuildFir/calls/syntheticResultDeclaration.txt

@@ -1,10 +1,9 @@
 KT element: KtCallExpression
-FIR element: FirPropertyImpl
+FIR element: FirFunctionCallImpl
 FIR source kind: KtRealSourceElementKind
 
 FIR element rendered:
-public final [ResolvedTo(BODY_RESOLVE)] val $$result: R|kotlin/Int| = R|/foo|()
+R|/foo|()
-    public [ResolvedTo(BODY_RESOLVE)] get(): R|kotlin/Int|
 
 FIR FILE:
 FILE: [ResolvedTo(IMPORTS)] syntheticResultDeclaration.kts

analysis/low-level-api-fir/testData/getOrBuildFir/calls/syntheticResultDeclarationInitializer.txt

@@ -1,18 +1,10 @@
 KT element: KtScriptInitializer
-FIR element: FirScriptImpl
+FIR element: FirPropertyImpl
 FIR source kind: KtRealSourceElementKind
 
 FIR element rendered:
-context(<script>@R|kotlin/script/templates/standard/ScriptTemplateWithArgs|)
+public final [ResolvedTo(BODY_RESOLVE)] val $$result: R|kotlin/Int| = R|/foo|()
-SCRIPT: [ResolvedTo(BODY_RESOLVE)] <script-syntheticResultDeclarationInitializer.kts>
+    public [ResolvedTo(BODY_RESOLVE)] get(): R|kotlin/Int|
-    [ResolvedTo(BODY_RESOLVE)] lval args: R|kotlin/Array<kotlin/String>|
-
-    public final [ResolvedTo(IMPLICIT_TYPES_BODY_RESOLVE)] fun foo(): R|kotlin/Int| {
-        ^foo Int(24)
-    }
-
-    public final [ResolvedTo(BODY_RESOLVE)] val $$result: R|kotlin/Int| = R|/foo|()
-        public [ResolvedTo(BODY_RESOLVE)] get(): R|kotlin/Int|
 
 FIR FILE:
 FILE: [ResolvedTo(IMPORTS)] syntheticResultDeclarationInitializer.kts

plugins/scripting/scripting-compiler/src/org/jetbrains/kotlin/scripting/compiler/plugin/services/FirScriptConfigurationExtensionImpl.kt

@@ -1,5 +1,5 @@
 /*
- * Copyright 2010-2023 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Copyright 2010-2024 JetBrains s.r.o. and Kotlin Programming Language contributors.
  * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
  */
 
@@ -20,7 +20,6 @@ import org.jetbrains.kotlin.fir.declarations.impl.FirDefaultPropertyGetter
 import org.jetbrains.kotlin.fir.declarations.primaryConstructorIfAny
 import org.jetbrains.kotlin.fir.declarations.utils.SCRIPT_SPECIAL_NAME_STRING
 import org.jetbrains.kotlin.fir.expressions.*
-import org.jetbrains.kotlin.fir.expressions.builder.buildLazyExpression
 import org.jetbrains.kotlin.fir.expressions.impl.FirSingleExpressionBlock
 import org.jetbrains.kotlin.fir.moduleData
 import org.jetbrains.kotlin.fir.resolve.providers.dependenciesSymbolProvider
@@ -157,13 +156,13 @@ class FirScriptConfiguratorExtensionImpl(
                     buildProperty {
                         this.name = Name.identifier(resultFieldName)
                         this.symbol = FirPropertySymbol(this.name)
-                        source = lastExpression.source
+                        source = lastScriptBlock?.source
                         moduleData = session.moduleData
                         origin = FirDeclarationOrigin.ScriptCustomization.ResultProperty
                         initializer = lastExpression
                         returnTypeRef = lastExpressionTypeRef
                         getter = FirDefaultPropertyGetter(
-                            lastExpression.source,
+                            lastScriptBlock?.source?.fakeElement(KtFakeSourceElementKind.DefaultAccessor),
                             session.moduleData,
                             FirDeclarationOrigin.ScriptCustomization.ResultProperty,
                             lastExpressionTypeRef,