Deprecate SuggestionSpan#ACTION_SUGGESTION_PICKED

This CL deprecates SuggestionSpan#ACTION_SUGGESTION_PICKED and related
constants [1].

There are multiple security concerns, open questions about
compatibility, and maintainance challanges in this protocol.

IME developers can implement their own suggestion picker UI on top of
CursorAnchorInfo API to achieve safer, should give more flexible UI
options, better security, and better compatibility.

 [1]: Ia539de0acf66053e0349daec459d75e36805f6bf
      f9f01008

Fix: 123160396
Test: make -j checkbuild
Change-Id: I6d39e838ae47488055162cd44b5f553f68869b17