UI: Adjust styling of QTabBar tabs

[Warchamp7]

Description

Adjusts the appearance of tabs in tab bar widgets such as the Output tab and stacked docks.

Before:

After:

Motivation and Context

Feedback on Discord

How Has This Been Tested?

👁

Types of changes

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

Checklist:

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