frontend: Remove sender() usage from UI handlers

[xakep8]

Description

Fixes #13444

Pass source and editor context explicitly instead of recovering it through QObject::sender().

Motivation and Context

QObject::sender() is fragile in its implementation as it relies on the runtime knowledge of the sender as well as dynamic properties rather than type-safe and explicit message flows. The calling sites know where the call is from since the connections were made, and thus this information can be passed directly.

How Has This Been Tested?

xcodebuild -configuration RelWithDebInfo -scheme obs-studio -parallelizeTargets -destination "generic/platform=macOS,name=Any Mac"

Types of changes

• Code cleanup (non-breaking change which makes code smaller or more readable)

Checklist:

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