By setting the ncurses_builtin_key_parser ui_option to true, we
can disable ncurses parsing of key strokes to get less portable
parsing but support for more complex modifiers.
Final is more granular, it consists of FinalFg (f), FinalBg (g)
and FinalAttr (a) which control if a face's fg, bg, or attributes
fully overwrite the previous face (instead of merging) and if
following faces apply on top of this face or not.
Fixes#2388 if the Whitespace face has the FinalFg flag.
Automatic reparsing of %sh{...}, while convenient in many cases,
can be surprising as well, and can lead to security problems:
'echo %sh{ printf "foo\necho bar" }' runs 'echo foo', then 'echo bar'.
we make this danger explicit, and we fix the 'nop %sh{...}' pattern.
To reparse %sh{...} strings, they can be passed to evaluate-commands,
which has been fixed to work in every cases where %sh{...} reparsing
was used..
