frontend, libobs: Add OBSProperties OBSPtr type

[cg2121]

Description

We no longer have to manually destroy obs_properties_t.

Motivation and Context

RAII is better

How Has This Been Tested?

Opened properties in different places of OBS to make sure nothing broke.

Types of changes

• Code cleanup (non-breaking change which makes code smaller or more readable)

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.