Refactor TextViewContextMenuTest

Some improvements to the test:
 - No need to rely on creating an activity anymore, so removed.
 - Test time improved ~10x

Bug: 345709107
Flag: EXEMPT minor refactoring to test only.
Test: atest TextViewContextMenuTest

Change-Id: I95e5fa397918b97fe0a983793c6d0d9ffad41ba6