CI: Update Github Actions with caching and macOS improvements

libobs-winrt: win-capture: Detect GraphicsCaptureItem closure

Make WGC window capture recover from GraphicsCaptureItem closure, which
can occur when following links in fullscreen Chrome for example.

A long standing lack of synchronization on the elevated process handle
made the non-elevated process always exit, so the updater would assume
it was started elevated and launch OBS from the elevated context.

Also applies the altered working directory to the non-elevated code
path so it can find the OBS executable properly.

libobs: Don't allow duplicating scene sources

deps/glad: Fix build with GCC-10

GCC-10 defaults to '-fno-common' [1], which triggers issues with
defining global variables multiple times.  To fix the build, use
'extern' to turn the first definition of 'gladGetProcAddressPtr'
into a declaration.

1. https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85678

Closes https://github.com/obsproject/obs-studio/issues/2828

vlc-video: Add procedure to receive media metadata

rtmp-services: Add Xlovecam.com streaming service

libobs: Additionally use SetThreadDescription if possible

Closes obsproject/obs-studio#2813

obs-plugins: Check if sources are showing for media hotkeys

obs-scripting: Expose platform functions to scripts

rtmp-services: Update GameTips.TV

It's the better way to declare thread names, but you need Windows 10,
version 1607 to use it.

libobs: Add Windows 10 release version to crash log

Original code makes duplicated item and bad memory

Closes obsproject/obs-studio#2837

libobs-opengl: Lock Mac parent context during present

Closes obsproject/obs-studio#2843

Parent context lock keeps GL commands serialized.

Fixes race that causes crash when resizing multiview.

Follow-up to eadb96fb.

obs-ffmpeg: Update error message in process_packet

rtmp-services: Add Nimo TV

The error message in the process_packet function was prefixed with
"receive_audio" because it was previously from code in the encode_audio
function which was called from the receive_audio function. This is just
a string change to avoid being misled to believe that the error is
always audio related.

vlc-video: Enable building the plugin on FreeBSD

This fixes an issue where an encoder may error out on a path that
doesn't use obs_encoder_set_last_error, resulting in a stale error being
used.

If we fallback to ffmpeg NVENC, the error from new NVENC might still be
present in the encoder structure. Given that this provides a lot more
actionable information to the user, let's use it if possible.

Fixes https://github.com/obsproject/obs-studio/issues/2807