Today the reader exposes its internals directly, e.g. to the commandline
builtin. This is of course not thread safe. For example in concurrent
execution, running `commandline` twice in separate threads would cause a
race and likely a crash.
Fix this by factoring all the commandline state into a new type
'commandline_state_t'. Make it a singleton (there is only one command
line
after all) and protect it with a lock.
No user visible change here.
This can easily lead to an infinite loop, if a variable handler
triggers a repaint and the variable is set in the prompt, e.g. some of
the git variables.
A simple way to reproduce:
function fish_mode_prompt
commandline -f repaint
end
Repainting executes the mode prompt, which triggers a repaint, which
triggers the mode prompt, ....
So we just set a flag and check it.
Fixes#7324.
