Move TextClassifier.getLocalTextClassifier() API.

In the future, we think the TextClassifier is going to run in an
external process. This CL moves the getLocalTextClassifier() API so
that we don't have to guarantee this to apps.
OEMs implementing TextClassifierServices however will want access to
this API so this CL effectively moves the the API from where apps
typically look for a TC (we prefer apps to call getTextClassifier()
instead) to where TCS implementations are most likely to be accessing
such APIs. The method is also renamed appropriately to what it will be
long term (i.e. the default TC implementation rather than as the local
TC).

Bug: 123681286
Test: atest core/tests/coretests/src/android/view/textclassifier
Test: atest cts/tests/tests/view/src/android/view/textclassifier/cts
Test: adb shell am instrument -w -e class android.textclassifier.TextClassifierPerfTest com.android.perftests.core/androidx.test.runner.AndroidJUnitRunner
Change-Id: I685e2b5263ffddbe301256fc2ed0d6254c3357ed