New AccessibilityService API to talk with HID Braille Displays.

API is implemented behind flag android.view.accessibility.braille_display_hid

Bug: 303522222
Bug: 316035785
Test: CTS: atest BrailleDisplayTest
      Internal: atest BrailleDisplayConnectionTest
                atest AccessibilityServiceConnectionTest
Change-Id: Ia775750ed6c11da1b21983ec70b035039f1df665