[FIR] Display actual type for argument type mismatch error

Previously the argument type was being used for the actual type error
display. However, safe-call arguments are unwrapped which causes
nullable types to be displayed as non-null. Change to use the actual
type provided by the diagnostic instead of extracting the type from
the argument.

#KT-58844 Fixed

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirLightTreeOldFrontendDiagnosticsTestGenerated.java

@@ -22744,6 +22744,12 @@ public class FirLightTreeOldFrontendDiagnosticsTestGenerated extends AbstractFir
                 runTest("compiler/testData/diagnostics/tests/nullableTypes/inferenceFlexibleTToNullable.kt");
             }
 
+            @Test
+            @TestMetadata("kt58844.kt")
+            public void testKt58844() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/nullableTypes/kt58844.kt");
+            }
+
             @Test
             @TestMetadata("nullAssertOnTypeWithNullableUpperBound.kt")
             public void testNullAssertOnTypeWithNullableUpperBound() throws Exception {

compiler/fir/analysis-tests/tests-gen/org/jetbrains/kotlin/test/runners/FirPsiOldFrontendDiagnosticsTestGenerated.java

@@ -22750,6 +22750,12 @@ public class FirPsiOldFrontendDiagnosticsTestGenerated extends AbstractFirPsiDia
                 runTest("compiler/testData/diagnostics/tests/nullableTypes/inferenceFlexibleTToNullable.kt");
             }
 
+            @Test
+            @TestMetadata("kt58844.kt")
+            public void testKt58844() throws Exception {
+                runTest("compiler/testData/diagnostics/tests/nullableTypes/kt58844.kt");
+            }
+
             @Test
             @TestMetadata("nullAssertOnTypeWithNullableUpperBound.kt")
             public void testNullAssertOnTypeWithNullableUpperBound() throws Exception {

compiler/fir/checkers/src/org/jetbrains/kotlin/fir/analysis/diagnostics/coneDiagnosticToFirDiagnostic.kt

@@ -223,7 +223,7 @@ private fun mapInapplicableCandidateError(
                 FirErrors.ARGUMENT_TYPE_MISMATCH.createOn(
                     rootCause.argument.source ?: source,
                     rootCause.expectedType.removeTypeVariableTypes(typeContext),
-                    rootCause.argument.typeRef.coneType.removeTypeVariableTypes(typeContext),
+                    rootCause.actualType.removeTypeVariableTypes(typeContext),
                     rootCause.isMismatchDueToNullability
                 )
             }