[Blinking Text Cursor Setting] Add labels for slider state descriptions

* Add values to label the slider with corresponding state descriptions
with a percentage change in relation to the default (500 ms).

Flag: android.view.accessibility.text_cursor_blink_interval
Bug: 423943893
Bug: 385781377
Bug: 402134144
Test: Tested locally and validated that Talkback reads the correct
slider state descriptions.

Change-Id: I13266b006abf7d62c37748f5b659b0a6bc5776e5