Rename LockscreenLongPress to LockscreenTouchHandling

Update the name and comments as the composable handles single tap,
double tap, and long press inputs.

Bug: 394952486
Test: atest SystemUiRoboTests
Test: manual - enable AConfig and double tap setting and verify
double tapping in empty space on lock screen goes to sleep
Flag: com.android.systemui.double_tap_to_sleep

Change-Id: I1261d907a5846d3550ec8e6a16ed5ed89bdf3dd0