The mapping from scancodes to the indexes used in xrdp_keymap
is not well designed and contains an implicit dependency on
keycode values.
This mapping is alse slightly different from the index used for
the 'keys' map in the xrdp_wm structure.
This commit introduces support for mapping scancodes directly
to 'scancode indexes' suitable for indexing into both structures.
Some renaming is also done; [MS-RDPBCGR] uses the terms scancode
and keyCode interchangeably. An effort is made to use key_code for a
raw value from a TS_KEYBOARD_EVENT, and scancode for a value which is
produced by the scancode module.
matt335672