Align the Talkback slider percentage announcement with the UI.

- Revert ag/21912040. That CL doesn't fix b/264841237 anyway. The
problem is that `INITIAL_PROGRESS` was not used in all the conversions.
- Call `mSeekBar.setStateDescription` with the same value as
`mVolumeValueText.setText` This ensures consistency between the UI and
the Talkback announcement.

Flag: EXEMPT bugfix
Bug: 374860822
Test: locally on a physical device.
Change-Id: Ib2904d8ed4f067ff50a28ac682a6f260c428d641