docs: Update TextView JavaDoc comments

- fix typographic errors (misspellings)
- Simplified the overview to essential info
- included a code example for common TextView usecase
- adds missing javadoc description and param for setScroller method

From BNR vendor, Project 01, android-developer-documentation/pull/1
Test: docs-only change. Tested with a check build

Change-Id: Id853c5587722c7125a33e25002e2bde73e397c0d