Some bluetooth keyboards [1] input U+02C6, the unicode character
MODIFIER LETTER CIRCUMFLEX ACCENT instead of the more common ^
(U+005E CIRCUMFLEX ACCENT). Remap it to the common caret since
that is what terminal programs expect.
[1] https://plus.google.com/100972300636796512022/posts/f7PKpXWesgG
The original reason for intercepting the escape key in onKeyPreIme()
was to prevent the escape key as being treated as the Back key before
reaching onKeyDown().
This seems no long necessary, and may mess up handling the ...+1
combination for escape on the Google Pixel C keyboard (see #27).