kernel32/tests: Add UTF-7 stray + sign removal tests.
kernel32/tests: Add UTF-7 implicit termination tests.
kernel32/tests: Add tabular UTF-7 decoding tests.
kernel32: Support UTF-7 in WideCharToMultiByte.

Portions of utf7_wcstombs were written by Sebastian Lackner
<sebastian@fds-team.de>
kernel32: Support UTF-7 in MultiByteToWideChar.

Portions of utf7_mbstowcs were written by Sebastian Lackner
<sebastian@fds-team.de>