Focus on search field when Autocomplete is opened

[johan12345]

This fixes #1011, based on @langsmith's commit https://github.com/mapbox/mapbox-plugins-android/commit/0c64cf98a75eb3cf3f0d4f3470ac56e1e9caab0d. PR #968, which contained this commit as well as other changes, has been closed as stale.

As fixing #1011 is a very basic need for an autocomplete field and only needs 2 lines of code, maybe this can be solved more quickly with this separate PR.