fix(ivy): injectable pipe schematic generating incorrect import statements (#30170)

Currently the injectable pipe schematic generates invalid imports like `import import { Pipe, PipeTransform, Injectable } from '@angular/core'; from '@angular/core';`. The issue wasn't caught by the unit tests, because the invalid import still contains the valid one.

Fixes #30159.

PR Close #30170

packages/core/schematics/test/google3/injectable_pipe_spec.ts

@@ -85,7 +85,10 @@ describe('Google3 injectable pipe TSLint rule', () => {
     `);
 
     runTSLint();
-    expect(getFile('/index.ts')).toContain('import { Pipe, Injectable } from \'@angular/core\'');
+
+    const content = getFile('/index.ts');
+    expect(content).toContain('import { Pipe, Injectable } from \'@angular/core\'');
+    expect((content.match(/import/g) || []).length).toBe(1, 'Expected only one import statement');
   });
 
 });

packages/core/schematics/test/injectable_pipe_migration_spec.ts

@@ -70,8 +70,10 @@ describe('injectable pipe migration', () => {
     `);
 
     runMigration();
-    expect(tree.readContent('/index.ts'))
-        .toContain('import { Pipe, Injectable } from \'@angular/core\'');
+
+    const content = tree.readContent('/index.ts');
+    expect(content).toContain('import { Pipe, Injectable } from \'@angular/core\'');
+    expect((content.match(/import/g) || []).length).toBe(1, 'Expected only one import statement');
   });
 
   it('should not add an import for Injectable if it is imported already', () => {