UI: Use keychain APIs for OAuth credentials

[derrod]

Description

This is built on top of #9122 as a test/reference implementation for using the keychain APIs. It will require some rework whenever obsproject/rfcs#39 is done.

Motivation and Context

More secure credentials storage and good practice of revoking credentials once they're no longer neeed.

How Has This Been Tested?

Tested on Windows, Mac, and Linux.

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

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

[Fenrirthviti]

Since this has an open and pending RFC as a requirement, we are opting to close this until the RFC has been finalized.

The branch and discussion on implementation is welcome to take place on the RFC, and this may be reopened when the RFC is finalized.