fix(@ngtools/webpack): elide type only named imports when using emitDecoratorMetadata

With this change we fix an issue where type only named imports were being emitted. As a result webpack failed to resolve such symbols as they don't exist in JavaScript.

Closes angular#23667

Author: alan-agius4

packages/ngtools/webpack/src/transformers/elide_imports.ts

@@ -153,7 +153,7 @@ export function elideImports(
         clausesCount += namedBindings.elements.length;
 
         for (const specifier of namedBindings.elements) {
-          if (isUnused(specifier.name)) {
+          if (specifier.isTypeOnly || isUnused(specifier.name)) {
             removedClausesCount++;
             // in case we don't have any more namedImports we should remove the parent ie the {}
             const nodeToRemove =

packages/ngtools/webpack/src/transformers/elide_imports_spec.ts

@@ -440,6 +440,44 @@ describe('@ngtools/webpack transformers', () => {
         experimentalDecorators: true,
       };
 
+      it('should elide type only named imports', () => {
+        const input = tags.stripIndent`
+          import { Decorator } from './decorator';
+          import { type OnChanges, type SimpleChanges } from './type';
+
+          @Decorator()
+          export class Foo implements OnChanges {
+            ngOnChanges(changes: SimpleChanges) { }
+          }
+
+          ${dummyNode}
+        `;
+
+        const output = tags.stripIndent`
+          import { __decorate } from "tslib";
+          import { Decorator } from './decorator';
+
+          let Foo = class Foo { ngOnChanges(changes) { } };
+          Foo = __decorate([ Decorator() ], Foo);
+          export { Foo };
+        `;
+
+        const { program, compilerHost } = createTypescriptContext(
+          input,
+          additionalFiles,
+          true,
+          extraCompilerOptions,
+        );
+        const result = transformTypescript(
+          undefined,
+          [transformer(program)],
+          program,
+          compilerHost,
+        );
+
+        expect(tags.oneLine`${result}`).toEqual(tags.oneLine`${output}`);
+      });
+
       it('should not remove ctor parameter type reference', () => {
         const input = tags.stripIndent`
           import { Decorator } from './decorator';