frontend: Fix volume control resizing and menu warning

[Warchamp7]

Description

First commit changes the sizeHint and resize behaviour so that the VolumeName widget properly tries to ellide text when it can't fit AND a sizePolicy has been set that allows it to shrink. It also increases the maximum width of the widget in the horizontal mixer layout.

Second commit fixes a warning when showing the audio mixer menu popup.

Motivation and Context

Better use of space for horizontal mixer and better behaviour of the VolumeName widget.

Before	After
obs64_dfj20LdNlr.mp4	obs64_ObFgAfmkW4.mp4

Also warnings are bad.

How Has This Been Tested?

👁

Types of changes

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

• Tweak (non-breaking change to improve existing functionality)

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 has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.