feat(language-service): Add diagnostics to suggest turning on strict mode (#40423)

This PR adds a way for the language server to retrieve compiler options
diagnostics via `languageService.getCompilerOptionsDiagnostics()`.

This will be used by the language server to show a prompt in the editor if
users don't have `strict` or `fullTemplateTypeCheck` turned on.

Ref https://github.com/angular/vscode-ng-language-service/issues/1053

PR Close #40423

packages/compiler-cli/src/ngtsc/core/api/src/public_options.ts

@@ -127,9 +127,9 @@ export interface StrictTemplateOptions {
   /**
    * If `true`, implies all template strictness flags below (unless individually disabled).
    *
-   * Has no effect unless `fullTemplateTypeCheck` is also enabled.
+   * This flag is a superset of `fullTemplateTypeCheck`.
    *
-   * Defaults to `false`, even if "fullTemplateTypeCheck" is set.
+   * Defaults to `false`, even if "fullTemplateTypeCheck" is `true`.
    */
   strictTemplates?: boolean;
 

packages/compiler-cli/src/ngtsc/core/src/compiler.ts

@@ -906,7 +906,7 @@ function getR3SymbolsFile(program: ts.Program): ts.SourceFile|null {
 
 /**
  * Since "strictTemplates" is a true superset of type checking capabilities compared to
- * "strictTemplateTypeCheck", it is required that the latter is not explicitly disabled if the
+ * "fullTemplateTypeCheck", it is required that the latter is not explicitly disabled if the
  * former is enabled.
  */
 function verifyCompatibleTypeCheckOptions(options: NgCompilerOptions): ts.Diagnostic|null {

packages/compiler-cli/src/ngtsc/diagnostics/src/error_code.ts

@@ -159,6 +159,16 @@ export enum ErrorCode {
    * An injectable already has a `ɵprov` property.
    */
   INJECTABLE_DUPLICATE_PROV = 9001,
+
+  // 10XXX error codes are reserved for diagnostics with category
+  // `ts.DiagnosticCategory.Suggestion`. These diagnostics are generated by
+  // language service.
+
+  /**
+   * Suggest users to enable `strictTemplates` to make use of full capabilities
+   * provided by Angular language service.
+   */
+  SUGGEST_STRICT_TEMPLATES = 10001,
 }
 
 /**