[Analysis API FIR] support generated temp properties

KTIJ-23492 (array index expression), KTIJ-23138 (inc/dec desugaring)

compiler/fir/raw-fir/raw-fir.common/src/org/jetbrains/kotlin/fir/builder/BaseFirBuilder.kt

@@ -810,7 +810,7 @@ abstract class BaseFirBuilder<T>(val baseSession: FirSession, val context: Conte
             val indexVariables = indices.mapIndexed { i, index ->
                 generateTemporaryVariable(
                     baseModuleData,
-                    index.toFirSourceElement(),
+                    index.toFirSourceElement(KtFakeSourceElementKind.ArrayIndexExpressionReference),
                     name = SpecialNames.subscribeOperatorIndex(i),
                     index.convert()
                 ).also { statements += it }

compiler/frontend.common/src/org/jetbrains/kotlin/KtSourceElement.kt

@@ -163,6 +163,11 @@ sealed class KtFakeSourceElementKind : KtSourceElementKind() {
     // list[0] -> list.get(0) where name reference will have a fake source element
     object ArrayAccessNameReference : KtFakeSourceElementKind()
 
+    // a[b]++
+    // b -> val <index0> = b where b will have fake property
+    object ArrayIndexExpressionReference : KtFakeSourceElementKind()
+
+
     // super.foo() --> super<Supertype>.foo()
     // where `Supertype` has a fake source
     object SuperCallImplicitType : KtFakeSourceElementKind()