Refine FloatingToolbarPopup to allow multiple implementations

This change refined the FloatingToolbarPopup to allow the local and
system implementation. Use the flag to control which implementation
will be used. Use the local implementation as default, we will switch
the system version when it is done and stable.

Bug: 190030331
Bug: 205822301
Test: manual. The toolbar still work after refinement
Test: atest TextViewActivityTest
Test: atest TextViewIntegrationTest
Ignore-AOSP-First: new feature for T.

Change-Id: I191cb02fc4857855f5b63bdab21c014fa0879a0c