FIR IDE: implement assignment statement references

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/checkers/extended/UnusedChecker.kt

@@ -256,7 +256,6 @@ object UnusedChecker : FirControlFlowChecker() {
             vararg qualifiedAccesses: FirQualifiedAccess,
         ): PathAwareVariableStatusInfo {
             fun retrieveSymbol(qualifiedAccess: FirQualifiedAccess): FirPropertySymbol? {
-                if (qualifiedAccess.source?.kind is FirFakeSourceElementKind) return null
                 val reference = qualifiedAccess.calleeReference as? FirResolvedNamedReference ?: return null
                 val symbol = reference.resolvedSymbol as? FirPropertySymbol ?: return null
                 return if (symbol !in localProperties) null else symbol

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

@@ -873,8 +873,9 @@ abstract class BaseFirBuilder<T>(val baseSession: FirSession, val context: Conte
             return buildAssignmentOperatorStatement {
                 source = baseSource
                 this.operation = operation
-                // TODO: take good psi
-                leftArgument = this@generateAssignment?.convert() ?: buildErrorExpression {
+                leftArgument = withDefaultSourceElementKind(FirFakeSourceElementKind.DesugaredCompoundAssignment) {
+                    this@generateAssignment?.convert()
+                } ?: buildErrorExpression {
                     source = null
                     diagnostic = ConeSimpleDiagnostic(
                         "Unsupported left value of assignment: ${baseSource?.psi?.text}", DiagnosticKind.ExpressionRequired

compiler/fir/resolve/src/org/jetbrains/kotlin/fir/resolve/transformers/body/resolve/FirExpressionsResolveTransformer.kt

@@ -353,7 +353,7 @@ open class FirExpressionsResolveTransformer(transformer: FirBodyResolveTransform
             explicitReceiver = leftArgument
             argumentList = buildUnaryArgumentList(rightArgument)
             calleeReference = buildSimpleNamedReference {
-                source = assignmentOperatorStatement.source
+                source = assignmentOperatorStatement.source?.fakeElement(FirFakeSourceElementKind.DesugaredCompoundAssignment)
                 this.name = name
                 candidateSymbol = null
             }