[Android DomKey] Emit VKEY_RETURN for AKEYCODE_NUMPAD_ENTER

Problem:

On an Android device with a connected hardware keyboard,
pressing the numpad enter button does not result in a form
submit.

Solution:

On the Android-to-DOM keycode map, add a case for
AKEYCODE_NUMPAD_ENTER to return VKEY_ENTER.

This makes AKEYCODE_NUMPAD_ENTER behave the same way as the
existing AKEYCODE_ENTER and AKEYCODE_DPAD_CENTER maps to
VKEY_ENTER, allowing for form submits.

This aligns with the DOM-to-Android keycode map, which
already maps the following Android keycodes to DOM
VKEY_ENTER:
- AKEYCODE_ENTER
- AKEYCODE_DPAD_CENTER
- AKEYCODE_NUMPAD_ENTER

TEST=Manual
1. Connect a hardware keyboard to an Android device.
   (Or use adb shell input keyevent KEYCODE_NUMPAD_ENTER)
2. Open the following URL on the Android device:
https://w3c.github.io/uievents/tools/key-event-viewer.html
3. With the cursor on the input field, press the numpad
   enter button on the keyboard.

Without the change:
No "beforeinput" event is emitted, indicating that a form
submit would have NOT occurred.

With the change:
A "beforeinput" event is emitted, indicating that a form
submit would have occurred.

This manual test case can also be done on any arbitrary
form field (e.g. login pages).

Automated:

$ ./out/Debug/bin/run_events_unittests -v -f \
  *AndroidKeyCodeToKeyboardCode*

BUG=41461362

Change-Id: I936c7f1319090e1f69214a348c444731d1c48015
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6774007
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1490275}