This implements OSC 4, 10, 11 - change <color>/foreground/background,
and their corresponding 'query' variant (which was already implemented
for OSC 10/11).
It also implements OSC 104, 110, 111 - reset
<color>/foreground/background.
Set corresponding terminfo entries to signal this support to clients.
I.e. it issues a \E[2 q regardless of what we've configured the
terminfo Se entry to.
So, make \E[2 q mean "the user configured cursor style" (which
defaults to 'block').
According to the specs, \E[0 q means a blinking block cursor. However,
since it also states that \E[1 q *also* is a blinking block cursor,
and that it is the default, *and* given that fact that parameter-less
CSIs typically means "reset", let's make it mean "reset to the user
configured cursor style".
Use our own escape sequence for the 'flash' terminfo entry.
Implemented by arming a timer FD and setting a boolean that indicates
we're currently "flashing".
The renderer draws a semi-transparent yellowish layer over the entire
window when "flashing" is active.
22;0|1|2t pushes the current window title/icon to the stack, while 23
pops it.
The second parameter, 0|1|2 has the following meaning:
0 - push/pop icon+title
1 - push/pop icon
2 - push/pop title
