cmake: Fix handling of debug wrapper libraries

[PatTheMav]

Description

Fix and simplify handling of CEF wrapper libraries in debug build configuration.

Motivation and Context

Specifying separate targets for debug configuration (as well as using "debug" and "optimized" keywords) is legacy behavior.

The correct way is to specify _DEBUG variants of the imported target properties, which CMake will pick up automatically if the project is built with debug configuration.

This commit forward-fixes the update on obs-studio, by still using the legacy behavior if the legacy target is present.

How Has This Been Tested?

• Tested only locally, but needs to be tested with obs-studio and a pending PR on the main repo.

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.