An ExecDomain is a variation on WslDomain with the key difference
being that you can control how to map the command that would be
executed.
The idea is that the user can define eg: a domain for a docker
container, or a domain that chooses to run every command in its
own cgroup.
The example below shows a really crappy implementation as a
demonstration:
```
local wezterm = require 'wezterm'
return {
exec_domains = {
-- Commands executed in the woot domain have "WOOT" echoed
-- first and are then run via bash.
-- `cmd` is a SpawnCommand
wezterm.exec_domain("woot", function(cmd)
if cmd.args then
cmd.args = {
"bash",
"-c",
"echo WOOT && " .. wezterm.shell_join_args(cmd.args)
}
end
-- you must return the SpawnCommand that will be run
return cmd
end),
},
default_domain = "woot",
}
```
This commit unfortunately does more than should go into a single
commit, but I'm a bit too lazy to wrangle splitting it up.
* Reverts the nil/null stuff from #2177 and makes the
`ExtendSelectionToMouseCursor` parameter mandatory to dodge
a whole load of urgh around nil in table values. That is
necessary because SpawnCommand uses optional fields and the
userdata proxy was making that a PITA.
* Adds some shell quoting helper functions
* Adds ExecDomain itself, which is really just a way to
to run a callback to fixup the command that will be run.
That command is converted to a SpawnCommand for the callback
to process in lua and return an adjusted version of it,
then converted back to a command builder for execution.
refs: https://github.com/wez/wezterm/issues/1776
