Add browser dock functions in the frontend api

[tytan652]

Description

• Closes https://github.com/obsproject/obs-studio/pull/5679

Depends on:

• https://github.com/obsproject/obs-studio/pull/7636
• https://github.com/obsproject/obs-studio/pull/7637

Add function to the frontend API:

• Add obs_frontend_is_browser_available() to check if OBS Studio have the browser feature (built with obs-browser, not running under Wayland).
• Add obs_frontend_add_browser_dock() to add browser docks through the frontend API.
• Add obs_frontend_change_browser_dock_url() that allows to change the URL of an already existing browser dock (not a custom browser dock from the UI).

Motivation and Context

Finally land this feature.

Being able to use the browser from the frontend API is also a requirement of https://github.com/obsproject/rfcs/pull/39.

How Has This Been Tested?

Added a browser dock through the API.

Types of changes

• New feature (non-breaking change which adds 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.

[tytan652]

Might be superseded by #9220 browser related API for service integrations plugins