win32: Fix WSAStartup issues

win32: Fix WSAStartup issues

WSAStartup was not being called for pacat and pactl built with meson,
causing them to fail in pa_mainloop_new with "cannot create wakeup
pipe". This issue also affects other applications linking to libpulse
other than the pulseaudio daemon, which calls WSAStartup itself.

When built with autotools, WSAStartup would have been called in
DllMain, which is recommended against by the documentation [1].

To fix these issues, the WSAStartup/WSACleanup calls can be moved
into pa_mainloop_new/pa_mainloop_free.

[1] https://docs.microsoft.com/en-us/windows/win32/api/winsock/nf-winsock-wsastartup

Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/456>