Use keyCode before defaulting to unrecognized rime keycode

[LEOYoon-Tsaw]

Sometimes (e.g. in ABC Extended keyboard layout), Option + certain keys gives modifier letters, even with NSEvent.charactersIgnoringModifiers

For example, ⌥+6 gives U+02C6 "MODIFIER LETTER CIRCUMFLEX ACCENT"

Thus in these keyboard layouts, shortcuts like ⌥+6 will never work with Rime.

This proposal try to use raw key code before defaulting to unrecognized symbols, so that although Rime doesn't recognize U+02C6 as a key char, but instead, we use the key code of 6 for processing.

Testing: It works for the stated purpose, ⌥+6 works in ABC - Extended keyboard layout.

[LEOYoon-Tsaw]

@lotem you have a big stock of keyboards, do you think it is going to lead to unwanted side effects

[lotem]

test other layouts like dvorak French azerty

[LEOYoon-Tsaw]

I tried French AZERTY keyboard, it works well. But this is software switch, I don't know if a physically different keyboard will behave the same way

[lotem]

All modern physical keyboards speak the same protocol.

[lotem]

In R2ime the user's program need to clarify whether the key code or character is processed.

[LEOYoon-Tsaw]

Then I'll proceed with this PR, while looking forward to R²ime