Add INJECT_KEY_EVENTS permission

Adds a new privileged|signature permission that allows clients to
create and own a VirtualKeyboard which for inputting key injections
to the system. Injected events can be sent to any display.

DD: go/a11y-al-pk-dd

Bug: 402581709
Bug: 399464391
Test: N/A

Flag: com.android.hardware.input.create_virtual_keyboard_api

Change-Id: Iaeecb820778ba42376e8eb8e3af306c16b58f901