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

Closes #19234

(cherry picked from commit 8e11ad9)

Author: alan-agius4

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

@@ -48,7 +48,9 @@ export function elideImports(
 
     // Record import and skip
     if (ts.isImportDeclaration(node)) {
-      imports.push(node);
+      if (!node.importClause?.isTypeOnly) {
+        imports.push(node);
+      }
 
       return;
     }

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

@@ -41,6 +41,15 @@ describe('@ngtools/webpack transformers', () => {
       'service.ts': `
         export class Service { }
       `,
+      'type.ts': `
+        export interface OnChanges {
+          ngOnChanges(changes: SimpleChanges): void;
+        }
+
+        export interface SimpleChanges {
+          [propName: string]: unknown;
+        }
+      `,
     };
 
     it('should remove unused imports', () => {
@@ -530,6 +539,40 @@ describe('@ngtools/webpack transformers', () => {
         expect(tags.oneLine`${result}`).toEqual(tags.oneLine`${output}`);
       });
 
+      it('should remove type-only imports', () => {
+        const input = tags.stripIndent`
+          import { Decorator } from './decorator';
+          import { Service } from './service';
+          import type { OnChanges, SimpleChanges } from './type';
+
+          @Decorator()
+          class Foo implements OnChanges {
+            constructor(param: Service) { }
+            ngOnChanges(changes: SimpleChanges) { }
+          }
+
+          ${dummyNode}
+        `;
+
+        const output = tags.stripIndent`
+          import { __decorate, __metadata } from "tslib";
+          import { Decorator } from './decorator';
+          import { Service } from './service';
+
+          let Foo = class Foo {
+            constructor(param) { }
+            ngOnChanges(changes) { }
+          };
+
+          Foo = __decorate([ Decorator(), __metadata("design:paramtypes", [Service]) ], Foo);
+        `;
+
+        const { program, compilerHost } = createTypescriptContext(input, additionalFiles, true, extraCompilerOptions);
+        const result = transformTypescript(undefined, [transformer(program)], program, compilerHost);
+
+        expect(tags.oneLine`${result}`).toEqual(tags.oneLine`${output}`);
+      });
+
       describe('NGTSC - ShorthandPropertyAssignment to PropertyAssignment', () => {
         const transformShorthandPropertyAssignment = (context: ts.TransformationContext): ts.Transformer<ts.SourceFile> => {
           const visit: ts.Visitor = node => {