UI: Enable multiple audio tracks in Simple Output recording

[pkviet]

Description

This adds support for multiple audio tracks in Simple Output for recordings. This is enabled for all quality presets (including "Lossless") except "Same as Stream".
This is also enabled for the Replay Buffer.
An exception is made for flv recording format since it only allows a single audio track.
The recorded track (and streaming track) is then Track 1 as before.

Screenshots
lossless preset:

encoded presets:

flv:

same as stream preset:

Motivation and Context

Members of obs support team report that regularly people switch from Simple to Advanced output just to be able to record multi track audio.
It would be better though for many to stick to Simple output, since it is ... simpler.

How Has This Been Tested?

Recordings made with three tracks in Simple output for:

• lossless preset,
• encoded presets (except flv).
  Checked that flv & "same as stream" preset record track 1.

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[WizardCM]

Note to self: test Advanced Audio Properties.

[Fenrirthviti]

From internal discussions about this: Disappearing items is something we no longer want to present in OBS, so this will need to find a permanent location to live. Disabling the checkboxes might be a solution here, but we will probably need to have a larger discussion on how best to approach this from a UI/UX standpoint for the various options.

Having this PR open should push those conversations forward as a high priority (at least, for myself) for post-v28 features.

[Warchamp7]

Can we get a radio group selection for flv (and any other formats that don't support multiple audio tracks) instead of removing the checkboxes?

If we are hardcoded to track 1 for single track formats, I'd still like a radio group and simply have it disabled.

[pkviet]

Updated the PR to implement @Fenrirthviti & @Warchamp7 suggestions.
When a preset / container which is not compatible with multiple tracks is picked, radio buttons are greyed out (track 1 is displayed as selected since it's the default for Simple Output; capability to pick the track for flv is beyond the purview of this PR.)
See the updated screen captures in first post of the PR.

[pkviet]

PR Updated

• Due to RFC 45 being merged, there's been conflicts which I fixed and also some rewriting had to be done to accommodate
  the new opus encoders.

[pkviet]

Update

• Per request from @Fenrirthviti and @Warchamp7 , moved the track checkboxes below the audio encoder field.
  

• There is an incompatibility between mov container and opus codec, introduced by the addition of opus to the codecs in simple output recording in RFC 45-5: Allow selection of the audio codec/encoder #8090 ; this will be fixed later through UI: Disable incompatible codecs in settings #8498

[RytoEX]

Looks okay at a glance.

[Warchamp7]

Approved on my end

[pkviet]

Update

• discovered today that this Qt bug is fixed: https://bugreports.qt.io/browse/QTBUG-6864
• this allows now the use of a QtStackedWidgets, which makes for less code and cleaner. So I've switched to that.
• also added one commit to move the tracks in Advanced Output > Standard Recording per request of @Warchamp7 .
• also moved the video encoder field above that of audio encoder in Advanced Output > Standard Recording per request of @derrod
  

[RytoEX]

Looks fine at a glance.