Flags to enable/disable smart selection in EditText

1. smart_selection_enabled_for_edit_text
   Disables smart selection for editable text.
2. smart_selection_dark_launch
   Dark launch TextClassifierImpl.suggestSelection(...)
   In this mode we run the method, but never change the user's
   selection to measure the quality of the results based on what
   the user actually wanted.

Bug: 65959640
Test: Manually tested flags turn on/off feature with 'adb shell
settings put global' and GServices override.
Test: bit FrameworksCoreTests:android.provider.SettingsBackupTest
Change-Id: Iacc561c8ee004b0123de66ad1ee06b1f56b4e4b4