Allow users to turn off key repeats

Allow users to turn off key repeats. Add it as a setting and the
corresponding APIs to get/set key repeat enabled.
Key repeats will be a regular physical keyboard setting rather than an
a11y setting, so update the APIs to reflect that.

Bug: 336585002
Test: atest InputDispatcherKeyRepeatTest
Flag: com.android.input.flags.keyboard_repeat_keys
Change-Id: I2fb0f1746699b6be5748da41dd08ed8c38e96a5f