[Mac web keypress] Don't convert number pad keys to non-located codes

When building a web input key event, the Mac-specific code would use
the non-located key code for number pad key presses. As a result,
websites were unable to distinguish between key presses on the number
pad and key presses in the number row. This cl preserves the located
key codes for number pad key presses on the Mac.

Bug: 1282730
Test: out/Default/content_unittests \
    --gtest_filter=WebInputEventBuilderMacTest.NumPadMapping

Change-Id: Ib72f2709f1ff23e8dfa109a9a3020d63c9b93f80
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3787686
Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
Commit-Queue: Jayson Adams <shrike@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1032607}