Introduce separate callee expression for when with subject variable

'Subject.Error' is redundant.
'Subject.None' can be an object.
'Subject#dataFlowValue' can be a lateinit property.

TODO: fix
- parsing local extension properties in 'when' subject
- parsing destructuring declarations in 'when' subject
- non-completed calls in nested 'when' with subject variable
- non-completed calls for subject variable in 'in' pattern

compiler/tests/org/jetbrains/kotlin/checkers/DiagnosticsTestGenerated.java

@@ -22496,6 +22496,12 @@ public class DiagnosticsTestGenerated extends AbstractDiagnosticsTest {
                     doTest(fileName);
                 }
 
+                @TestMetadata("subjectVariableInIsPattern.kt")
+                public void testSubjectVariableInIsPattern() throws Exception {
+                    String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/when/withSubjectVariable/subjectVariableInIsPattern.kt");
+                    doTest(fileName);
+                }
+
                 @TestMetadata("unsupportedFeature.kt")
                 public void testUnsupportedFeature() throws Exception {
                     String fileName = KotlinTestUtils.navigationMetadata("compiler/testData/diagnostics/tests/when/withSubjectVariable/unsupportedFeature.kt");