pulseaudio: reconnect context when pulseaudio server restarts

[Jay-716]

For some reason, I sometimes restart the pulseaudio server (pipewire-pulse actually). But after restart, waybar's pulseaudio module just stop updating. The solution is to restart the whole waybar.
So I think it would be better if waybar itself could reconnect to pulseaudio server after it restarts.
The pulseaudio context connection would failed according to the documentation. So we can simply reconnect the context there.

Tested on waybar latest git version and pipewire-pulse 1.0.0

Fixes: #2619

PS: I am not so good at C++ actually. So I am sorry if I do something stupid. :)

[Jay-716]

I add a connectContext() function. I hope i do it right.
Btw, I think pa_context_set_state_callback() should be called before pa_context_connect().(it's reversed in the original code) Otherwise there may be a race condition, i.e. the context may connect too fast that the callback is not yet registered and then no callbacks will be called.
And should I change the comment style from // to /**/ to match the style of existing code?
Thanks for reviewing!

[Alexays]

LGTM, thx!