refactor(core): rename ngModuleDef to ɵmod (#33142)

Module defs are not considered public API, so the property
that contains them should be prefixed with Angular's marker
for "private" ('ɵ') to discourage apps from relying on def
APIs directly.

This commit adds the prefix and shortens the name from
ngModuleDef to mod. This is because property names
cannot be minified by Uglify without turning on property
mangling (which most apps have turned off) and are thus
size-sensitive.

PR Close #33142

packages/compiler-cli/src/ngtsc/annotations/test/ng_module_spec.ts

@@ -77,7 +77,7 @@ runInEachFileSystem(() => {
       if (detected === undefined) {
         return fail('Failed to recognize @NgModule');
       }
-      const moduleDef = handler.analyze(TestModule, detected.metadata).analysis !.ngModuleDef;
+      const moduleDef = handler.analyze(TestModule, detected.metadata).analysis !.ɵmod;
 
       expect(getReferenceIdentifierTexts(moduleDef.declarations)).toEqual(['TestComp']);
       expect(getReferenceIdentifierTexts(moduleDef.exports)).toEqual(['TestComp']);