quartz: make function keys work (again?)

quartz: make function keys work (again?)

The F keys have no unicode mapping, and UCKeyTranslate() returns
a bogus 0x10 as mapping to unicode. Instead of checking for this
random and undocumented return value, simply assign all function
keys explicitly. This patch also splits the ill-named "known_keys"
array into "modifier_keys" and "function_keys" which is much
more obvious.
(cherry picked from commit 55f9e5cbaf9c5f6761d7bce7a1672bc1552e2f07)