Add function to signal the browser source from JavaScript

[exeldro]

Description

adds void source_browser_signal(ptr source, string signal) to the global signal handler
adds void browser_signal(ptr source, string signal) to the signal handler of the browser source
in javascript you can signal a signal handler like this: window.obsstudio.signal("signal")

Motivation and Context

Allow JavaScript to send signals to plugins, without the need for an obs websocket connection
More generic solution replacing #423
The use case is my Markdown Source plugin. I want to me able to size the browser source to its contents provided by the markdown. I could hack a way by forcing obs-websocket enabled and getting the obs-websocket port and password from the settings and provide that to the the browser source, but I prefer a way that I don't have to force users to enable obs-websocket.

How Has This Been Tested?

On windows 11 with changes to the markdown source to allow it to resize it self

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.