a11y: Add first-time use dialog for key gestures (1/n)

This patch provides
* Implemented the repository
* Implemented the unittest and kosmos

Bug: b/410892855
Flag:com.android.hardware.input.enable_talkback_and_magnifier_key_gestures
Test: atest AccessibilityShortcutsImplTest
Change-Id: I77659997d530dbeda2e45aae675550f1727245c2