cmake: Update library and target names for qrcodegen

[RytoEX]

Description

qrcodegen is identified as such (without the "lib" prefix) and as the target "qrcodegencpp::qrcodegencpp" by the CMake package generated by obs-deps and the finders in obs-studio when using module fallback.

Motivation and Context

Want OBS Studio to build in Debug without issues. This is a follow-up to #1167.

How Has This Been Tested?

Tested OS(s):

• Windows 11 Tested using the updated finder at https://github.com/obsproject/obs-studio/pull/9601 for non-Debug builds to ensure the finder itself still works. The finder shouldn't be invoked on Windows in the end.

Types of changes

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

Checklist:

• [x] I have read the Contributing Guidelines.
• [x] All commit messages are properly formatted and commits squashed where appropriate.
• [x] My code is not on master or a release/* branch.
• [x] The code has been tested.
• [x] I have included updates to all appropriate documentation.