feat(language-service): modularize error messages (#35678)

This commit performs a modularization of the Language Service's existing
diagnostic messages. Such a modularization has two primary advantages:

- Centralization and decoupling of error messages from the code that
  generates them makes it easy to add/delete/edit diagnostic messages,
  and allows for independent iteration of diagnostic messages and
  diagnostic generation.
- Prepares for additional features like annotating the locations where a
  diagnostic is generated and enabling the configuration of which
  diagnostics should be reported by the language service.

Although it would be preferable to place the diagnostics registry in an
independent JSON file, for ease of typing diagnostic types as an enum
variant of 'ts.DiagnosticCategory', the registry is stored as an object.

Part of #32663.

PR Close #35678

packages/language-service/test/diagnostics_spec.ts

@@ -85,7 +85,7 @@ describe('diagnostics', () => {
       mockHost.override(TEST_TEMPLATE, template);
       const diags = ngLS.getSemanticDiagnostics(TEST_TEMPLATE);
       expect(diags.length).toBe(1);
-      expect(diags[0].messageText).toBe('Unable to resolve signature for call of method $any');
+      expect(diags[0].messageText).toBe('Unable to resolve signature for call of $any');
     }
   });
 
@@ -129,7 +129,7 @@ describe('diagnostics', () => {
       `);
       const diags = ngLS.getSemanticDiagnostics(TEST_TEMPLATE);
       expect(diags.length).toBe(1);
-      expect(diags[0].messageText).toBe(`Expected the operants to be of similar type or any`);
+      expect(diags[0].messageText).toBe(`Expected operands to be of similar type or any`);
     });
 
     it('should not report errors for matching exported type', () => {
@@ -228,7 +228,7 @@ describe('diagnostics', () => {
 
     it('should report numeric operator errors', () => {
       const diags = ngLS.getSemanticDiagnostics(EXPRESSION_CASES).map(d => d.messageText);
-      expect(diags).toContain('Expected a numeric type');
+      expect(diags).toContain('Expected a number type');
     });
   });