Make IME extract text fields public

InputMethodService uses the following IDs for extract view.
- R.id.inputExtractEditText
- R.id.inputExtractAction
- R.id.inputExtractAccessories
While the first one is public, others are not. It makes sense to make
all of the public so IMEs can customize it.

Bug: 210777608
Test: atest InputMethodServiceTest

Change-Id: I125767d67839293c0b0f40c750d0fb1bb77951e9