refactor: remove imports to individual files through module name

We can't import individual files through the module name because:

* We don't have these listed in the rollup globals
* These imports will break in the Angular package (due to limitation in APF).

Author: devversion

src/material-experimental/mdc-button/testing/button-harness.ts

@@ -8,7 +8,7 @@
 
 import {ComponentHarness, HarnessPredicate} from '@angular/cdk/testing';
 import {coerceBooleanProperty} from '@angular/cdk/coercion';
-import {ButtonHarnessFilters} from '@angular/material/button/testing/button-harness-filters';
+import {ButtonHarnessFilters} from '@angular/material/button/testing';
 
 
 /**

src/material-experimental/mdc-menu/testing/menu-harness.ts

@@ -9,7 +9,7 @@
 import {ComponentHarness, HarnessPredicate} from '@angular/cdk/testing';
 import {coerceBooleanProperty} from '@angular/cdk/coercion';
 import {MatMenuItemHarness} from './menu-item-harness';
-import {MenuHarnessFilters} from '@angular/material/menu/testing/menu-harness-filters';
+import {MenuHarnessFilters} from '@angular/material/menu/testing';
 
 /**
  * Harness for interacting with a MDC-based mat-menu in tests.

src/material-experimental/mdc-menu/testing/menu-item-harness.ts

@@ -8,7 +8,7 @@
 
 import {ComponentHarness, HarnessPredicate} from '@angular/cdk/testing';
 import {coerceBooleanProperty} from '@angular/cdk/coercion';
-import {MenuItemHarnessFilters} from '@angular/material/menu/testing/menu-harness-filters';
+import {MenuItemHarnessFilters} from '@angular/material/menu/testing';
 
 
 /**

src/material/menu/testing/menu-item-harness.ts

@@ -8,7 +8,7 @@
 
 import {ComponentHarness, HarnessPredicate} from '@angular/cdk/testing';
 import {coerceBooleanProperty} from '@angular/cdk/coercion';
-import {MenuItemHarnessFilters} from '@angular/material/menu/testing/menu-harness-filters';
+import {MenuItemHarnessFilters} from './menu-harness-filters';
 
 
 /**

src/material/radio/testing/radio-harness.ts

@@ -6,9 +6,9 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {ComponentHarness, HarnessPredicate} from '@angular/cdk/testing';
 import {coerceBooleanProperty} from '@angular/cdk/coercion';
-import {RadioButtonHarnessFilters, RadioGroupHarnessFilters} from '@angular/material/radio/testing/radio-harness-filters';
+import {ComponentHarness, HarnessPredicate} from '@angular/cdk/testing';
+import {RadioButtonHarnessFilters, RadioGroupHarnessFilters} from './radio-harness-filters';
 
 /**
  * Harness for interacting with a standard mat-radio-group in tests.