UI: Remove QFuture usage

[palana]

Description

Unbreak OBS builds using older Qt versions, since QFutures are broken on older Qt versions, even with the deadlock workaround (see #10929)

Motivation and Context

This is meant to fix #10929

Originally the workaround for bouncing continuations between threads seemed sufficient, but there are Qt versions where even creating a ready future and trying to observe it breaks/causes deadlocks

How Has This Been Tested?

Tested "Start Streaming" works and error conditions (e.g. invalid configs) are still handled appropriately

Types of changes

• Bug fix (non-breaking change which fixes an issue)

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.

[PatTheMav]

In general I'm in favour of using more C++ standard functionality instead of Qt variants if possible (and only rely on Qt variants when interacting with UI code) as this allows us to more easily decouple core functionality from the presentation layer.

[palana]

Split out the first commit to make code motion more visible vs actual changes

[RytoEX]

The parts that I understand look okay. This is mostly shuffling code and changing types. The user who reported #10929 said that this PR fixes that Issue. I would still welcome additional review.

[Chiitoo]

This seems to break legacy CMake configuration:

CMake Error at UI/cmake/legacy.cmake:285 (target_sources):
  Cannot find source file:

    qt-helpers.cpp
Call Stack (most recent call first):
  cmake/Modules/ObsHelpers.cmake:473 (include)
  UI/CMakeLists.txt:3 (legacy_check)

Is that to be expected and intentional?

Thank you!

[palana]

This seems to break legacy CMake configuration:

CMake Error at UI/cmake/legacy.cmake:285 (target_sources):
  Cannot find source file:

    qt-helpers.cpp
Call Stack (most recent call first):
  cmake/Modules/ObsHelpers.cmake:473 (include)
  UI/CMakeLists.txt:3 (legacy_check)

Is that to be expected and intentional?

Thank you!

@Chiitoo: not intentional, and not expected necessarily 😅

filed a follow-up PR to fix this at #10967

[RytoEX]

This seems to break legacy CMake configuration:

CMake Error at UI/cmake/legacy.cmake:285 (target_sources):
  Cannot find source file:

    qt-helpers.cpp
Call Stack (most recent call first):
  cmake/Modules/ObsHelpers.cmake:473 (include)
  UI/CMakeLists.txt:3 (legacy_check)

Is that to be expected and intentional?

Thank you!

While we'll fix this, please note that legacy CMake will be removed in the near future.

[Chiitoo]

While we'll fix this, please note that legacy CMake will be removed in the near future.

Yep, already getting into the new way of things.

Thanks!