Fixes "Toggle Preview" hotkeys from duplicating when profiles are
switched.  The hotkeys were not being unregistered.

libobs-d3d11: Bad indices in log output

GitHub: Add funding buttons

Fix bad logging for LogAdapterMonitors and LogD3DAdapters. Update
EnumD3DAdapters for consistency.

Normally, paired encoders are unpaired when they stop.  However, if the
pairing occurs before the encoders actually start, and the encoders
never actually end up starting, they are never unpaired, and that
pairing stays with them until the next time an output is started up
again.  That in turn can cause an output that uses one of the encoders
but not the other to not function correctly, and neither properly
"start" nor stop because the data is queued continually in the
interleaved packet array.

For example, let's say there are two outputs, two video encoders, and
one audio encoder.  This can be reproduced by using advanced output mode
and making the two outputs use separate video encoders while sharing
track 1's audio encoder.  If you start up the stream output first and it
fails to fully connect for whatever reason (bad server, bad stream key,
etc), then you start up the recording output, the recording output will
appear to be running, but will not stop when you hit "stop recording".
It will stay perpetually on "stopping recording" and will get stuck that
way.  This is because when the streaming output started, the streaming
output would initially pair video encoder A with audio encoder A before
the encoders actually fully started up (as the encoders do not fully
start up until a connection is successfully made), and when the
recording output starts up after that disconnection, audio encoder A
will wait for video encoder A rather than video encoder B because that
pairing was never actually cleared.

So, instead of pairing encoders when the output starts, wait until the
encoders themselves are being started and then pair the encoders at that
point in time.  This ensures that the encoders start up and will clear
their pairing when no longer in use.

UI: Fix issue where rec time left would show negative time

The recording time left timer was being called an unnecessary time,
in the stats constructor, when it should have only been started
when the recording starts.

libobs: Remove unreachable YUV decode paths

A previous refactoring to make DrawMatrix unnecessary has left behind
unreachable YUV conversions. Even if this code was somehow reachable,
DrawMatrix for YUV -> RGB doesn't exist anymore, so they would render
incorrectly anyway.

Minor cleanup

Variable was never used. Clean up both C++ and shader code.

Incoming texture is UNORM, so the value must already be saturated.

Lambda replacement was added, but old function was left behind.

Shuts down browser panels early to ensure that cookie data doesn't
necessarily get lost.

UI: Remove 5 file limit for drag & drop

(This commit also modifies the UI, obs-ffmpeg, and obs-output modules)

Fixes a long-time regression where the program would lock up if an
encode call fails.  Shuts down all outputs associated with the failing
encoder and displays an error message to the user.

Ideally, it would be best if a more detailed error could be displayed to
the user about the nature of the error, though the primary problem is
the encoder errors are typically not something the user would be able to
understand.  The current message is a bit of a generic error message;
improvement is welcome.

Another suggestion is to try to have the encoder restart seamlessly,
though it would take a significant amount of work to be able to make it
do something like that properly, and it sort of assumes that encoder
failures are sporadic, which may not necessarily be the case with some
hardware encoders on some systems.  It may be better just to use another
encoder in that case.  For now, seamless restart is ruled out.

UI: Dark theme consistency for Scenes vs Sources

- Selected but unfocused Source colour
- Scenes font
- Padding when editing Source name

UI: Fix hotkey theme issues

UI: Add hover color to hotkey icons

libobs/UI: Add Transition Previews

This commit adds a preview to the properties window for transitions.

The preview will play back the transition at the global transition
duration or the transitions fixed duration, between two private scenes
with an A and B label, and different background colors.

This commit adds a function to forcefully stop a transition, and to
increment/decrement the showing counter for a source with the MAIN_VIEW
type.

These functions are needed for the transition previews to work as
intended.

Closes obsproject/obs-studio#1639

Fix VAAPI CBR

libobs: UI: Remove Qt usage from graphics thread

libobs: Restore casts to fix Clang warnings

obs-outputs: Fix undefined MSG_NOSIGNAL

This fixes Xcode warning about detecting UI usage from another thread.

Define MSG_NOSIGNAL even if CRYPTO is not defined.

Clang doesn't like it if you convert T** to const T* const* without
casting even though it should be safe. Might be a C language thing.

Avoid sigpipe on writing to closed file descriptors

obs-frontend-api: Add method to trigger a Studio Mode transition