Add test to check that dot shorthands do not have an obvious type

This PR adds a test to confirm that the lint
`omit_obvious_local_variable_types` considers a dot shorthand to be an
expression whose type is not obvious. This is crucial because the dot
shorthand would no longer work if the context type is turned into `_`
because the type annotation is removed. Similarly for the lint
`omit_obvious_property_types`.

Fixes #60910
Change-Id: Ie31026286eb496c0cd76c7bb5ca64e04340b4aaa
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/434660
Commit-Queue: Phil Quitslund <[email protected]>
Reviewed-by: Phil Quitslund <[email protected]>

Author: eernstg

pkg/linter/test/rules/omit_obvious_local_variable_types_test.dart

@@ -58,6 +58,14 @@ class A {
     );
   }
 
+  test_dot_shorthand() async {
+    await assertNoDiagnostics(r'''
+f() {
+  int i = .parse('1');
+}
+''');
+  }
+
   test_forEach_inferredList() async {
     await assertDiagnostics(
       r'''

pkg/linter/test/rules/omit_obvious_property_types_test.dart

@@ -91,6 +91,12 @@ class C {
     );
   }
 
+  test_dot_shorthand() async {
+    await assertNoDiagnostics(r'''
+int i = .parse('1');
+''');
+  }
+
   test_genericInvocation_paramIsType_static() async {
     await assertNoDiagnostics(r'''
 T bar<T>(T d) => d;