Previously, we just ignored ansi vs dec modes (`?`-prefix) and just
responded to both requests most of the time using the number as the
unique value. This _kind of works_ because almost all DEC modes do not
overlap with ANSI modes, but some overlap (i.e. `insert`, ANSI mode 4).
This commit properly separates ANSI vs DEC modes and updates all of our
terminal sequences to handle both (where applicable -- some sequences
are explicitly DEC-only).
Fixes#641
xterm does not so there is an argument to not doing this but a lot of
other terminals do. Having this on by default makes things like less
scroll with the mouse wheel by default which is nice to have.
This makes a few major changes:
- cursor style on terminal is single source of stylistic truth
- cursor style is split between style and style request
- cursor blinking is handled by the renderer thread
- cursor style/visibility is no longer stored as persistent state on
renderers
- cursor style computation is extracted to be shared by all renderers
- mode 12 "cursor_blinking" is now source of truth on whether blinking
is enabled or not
- CSI q and mode 12 are synced like xterm
