Again, just for preapring an easier return from the parsing routine.

There is no need to specially flag a function key or editing key --
the keycode is indication enough in itself: outside of byte range.

Saving roughly twenty microseconds at startup.

Also, when a key string does not denote a Ctrl nor Meta nor Function key,
there is no point in assigning a keycode, because plain characters cannot
be used as a function shortcut.

The keycode is not a sequence; it is a single integer value.

And instead of using two key types, just use a bool to indicate whether
a keystroke involves Meta.

A keycode is either already in byte range (so there is nothing to do)
or it is not and it shouldn't be (so there is nothing to do either).

After initialization, the type of a key is never used nor needed
(other than for meta keys).

Accept the "Esc [ 1 n ~" and "Esc [ 2 n ~" sequences only when they
end with the "~" character, not with any character.

It is nicer to have a predictable cursor position and not see it hop
left and right on differently indented lines.

Those lines don't exist in that mode -- the relevant subwindows are
smaller, or have been made smaller just before.

This fixes https://savannah.gnu.org/bugs/?48635.

It will be initialized when a new code is started.

This fulfills https://savannah.gnu.org/bugs/?48154.

And hard-bind the keys Ctrl+Up and Ctrl+Down to these functions.

Unlike the paragraph-jumping code, these new functions disregard
any indentation, treating only blank lines as separators.  They
also do an automatic smart home when that option is set.

This fulfills https://savannah.gnu.org/bugs/?48291.

The bug with a leading wide character has been fixed since ncurses-5.9.

See https://savannah.gnu.org/bugs/?31743 for reference.