Mark stylus buttons mapppings as fallback

We don't have a way to determine if devices can actually report HID
usage keys. Marking them as fallback only.

Bug: 297094448
Bug: 317838112
Test: atest inputflinger_tests
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:45f626a154f66f4cceecaf6e32392741a00529a3)
Merged-In: I45710f9e6237c86613717fab779dbd7cc5c66c86
Change-Id: I45710f9e6237c86613717fab779dbd7cc5c66c86

data/keyboards/Generic.kl

@@ -430,19 +430,17 @@ key 658   MACRO_3
 key 659   MACRO_4
 
 # Keys defined by HID usages
-key usage 0x0c0067 WINDOW
-key usage 0x0c006F BRIGHTNESS_UP
-key usage 0x0c0070 BRIGHTNESS_DOWN
-key usage 0x0c0079 KEYBOARD_BACKLIGHT_UP
-key usage 0x0c007A KEYBOARD_BACKLIGHT_DOWN
-key usage 0x0c007C KEYBOARD_BACKLIGHT_TOGGLE
-key usage 0x0c0173 MEDIA_AUDIO_TRACK
-key usage 0x0c019C PROFILE_SWITCH
-key usage 0x0c01A2 ALL_APPS
-# TODO(b/297094448): Add stylus button mappings as a fallback when we have a way to determine
-#   if a device can actually report it.
-# key usage 0x0d0044 STYLUS_BUTTON_PRIMARY
-# key usage 0x0d005a STYLUS_BUTTON_SECONDARY
+key usage 0x0c0067 WINDOW                    FALLBACK_USAGE_MAPPING
+key usage 0x0c006F BRIGHTNESS_UP             FALLBACK_USAGE_MAPPING
+key usage 0x0c0070 BRIGHTNESS_DOWN           FALLBACK_USAGE_MAPPING
+key usage 0x0c0079 KEYBOARD_BACKLIGHT_UP     FALLBACK_USAGE_MAPPING
+key usage 0x0c007A KEYBOARD_BACKLIGHT_DOWN   FALLBACK_USAGE_MAPPING
+key usage 0x0c007C KEYBOARD_BACKLIGHT_TOGGLE FALLBACK_USAGE_MAPPING
+key usage 0x0c0173 MEDIA_AUDIO_TRACK         FALLBACK_USAGE_MAPPING
+key usage 0x0c019C PROFILE_SWITCH            FALLBACK_USAGE_MAPPING
+key usage 0x0c01A2 ALL_APPS                  FALLBACK_USAGE_MAPPING
+key usage 0x0d0044 STYLUS_BUTTON_PRIMARY     FALLBACK_USAGE_MAPPING
+key usage 0x0d005a STYLUS_BUTTON_SECONDARY   FALLBACK_USAGE_MAPPING
 
 # Joystick and game controller axes.
 # Axes that are not mapped will be assigned generic axis numbers by the input subsystem.