fix(core): missing-injectable migration should not update type definitions (#33286)

Currently the `missing-injectable` migration seems to add
`@Injectable()` to third-party classes in type definitions.

This not an issue in general since we do not generate broken code
by inserting a decorator into a type definition file. Though, we can
avoid adding the decorator since it won't have any effect and in
general we should not write to non source files of the compilation unit.

PR Close #33286

packages/core/schematics/test/missing_injectable_migration_spec.ts

@@ -380,7 +380,6 @@ describe('Missing injectable migration', () => {
           .toContain(`{ ${type}, Injectable } from '@angular/core`);
     });
 
-
     it(`should migrate multiple nested providers in same ${type}`, async() => {
       writeFile('/index.ts', `
         import {${type}} from '@angular/core';
@@ -689,5 +688,24 @@ describe('Missing injectable migration', () => {
       expect(tree.readContent('/service.ts'))
           .toMatch(/import { Inject, Injectable } from '@angular\/core';/);
     });
+
+    it('should not migrate provider classes in library type definitions', async() => {
+      writeFile('/node_modules/my-lib/index.d.ts', `
+        export declare class MyService {}
+      `);
+
+      writeFile('/index.ts', `
+        import {MyService} from 'my-lib';
+        import {Pipe, ${type}} from '@angular/core';
+                  
+        @${type}({${propName}: [MyService]})
+        export class TestClass {}
+      `);
+
+      await runMigration();
+
+      expect(warnOutput.length).toBe(0);
+      expect(tree.readContent('/node_modules/my-lib/index.d.ts')).not.toContain('@Injectable');
+    });
   }
 });