Add CTS tests for BrailleDisplayController APIs.

Uses a standard file for the hidraw device node instead of a real
character device file. This simplifies automated testing without
requiring an actual connected Braille display.

Bug: 303522222
Bug: 316035785
Test: atest BrailleDisplayControllerTest
Change-Id: Id195100007b56e015e51f7b7b2afa46d5a5695fa
3 files changed