The hexadecimal notation is a Luajit extension which is not compatible with Lua
5.1. While Lua 5.2 does support hexadecimal sequences, it is better to target
Lua 5.1 for maximum compatibility with Luajit(which has fully compatible with
5.1 API/ABI).
Background: Vim internally prefers to represent ALT/META chords as
single-byte keys, by setting the high bit of the key byte.
extract_modifiers() _discards_ the meta/alt modifier, but we need it for
libvterm and libtermkey.
Closes#2440Closes#3727Closes#2017
References #2277
References #2254https://github.com/neovim/neovim/issues/2017#issuecomment-140423557
> We [not libtermkey] are setting the high bit for some reason
https://github.com/neovim/neovim/issues/176#issuecomment-77834715
> libvtermkey requires the leading esc to parse alt/meta
https://github.com/neovim/neovim/pull/3246#issuecomment-136328450
> A program could do better than the current logic on some terminals, by
> asking for pure 8bit mode (S8C1T) and then immediately querying the
> mode again. If the result comes back as an 8bit single-byte CSI, then
> it can presume the mode setting was successful, and now the ESC prefix
> byte won't be seen in multibyte sequences; only as an Alt- prefix or
> a real Escape key. On such a terminal, it could therefore avoid
> needing to use that waiting timeout.
This change adds switch cases for K_FOCUSGAINED and K_FOCUSLOST to the
input handling functions in ex_getln.c and terminal.c. The handling is
identical to what's found in edit.c (just calling apply_autocmds).
If one enters cmdline-mode by feeding `:` and sends a focuslost event (by
leaving the window for example) the text `<FocusLost>` will be inserted
into the command line. There is similar behaviour in terminal mode. This
patch corrects this behavior to fire the apropriate autocmd instead.
Fixes#3714
