libobs: Add missing encoder API functions

[Error-String-Expected-Got-Nil]

Description

Adds the API functions obs_encoder_get_signal_handler and obs_encoder_get_proc_handler, both of which are mentioned in the API docs but are not actually implemented in the API. Encoders don't use signals for anything, but it was easy enough to include that I didn't see a reason not to.

Motivation and Context

Encoders already have a proc and signal handler stored internally, it simply isn't externally accessible due to the absence of these functions. As such, implementing custom extra functionality for encoders is somewhat difficult at present. There's minimal cost to adding these functions, and some nice possibilities opened up for plugin creators and future feature additions.

How Has This Been Tested?

Created an encoder in a plugin's load function, used function to get its proc handler, and found it did correctly return the encoder's proc handler.

Types of changes

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

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]

If this function doesn't really serve any practical purpose, why would you add the function instead of correcting the documentation? What is the actual use case for this?

[tt2468]

Encoders might have custom functionality via procs/signals that one may want to implement. I can think of some ideas in my head which would necessitate usage of these functions. The proc/signal handlers for encoders are already there, just not accessible via the frontend API like they are with most other OBS objects.

[Error-String-Expected-Got-Nil]

If this function doesn't really serve any practical purpose, why would you add the function instead of correcting the documentation? What is the actual use case for this?

I'm making this PR specifically because I wanted to use one of these functions in a plugin I'm making and it wasn't available, so yes, I think there is a use case.

[Fenrirthviti]

Can you provide an example?

To be clear, I don't want to imply I'm against this, I'm mostly just curious the use case, and having a practical example will help in review for others.

[Error-String-Expected-Got-Nil]

Can you provide an example?

To be clear, I don't want to imply I'm against this, I'm mostly just curious the use case, and having a practical example will help in review for others.

Mine is a little weird, but the plugin I'm making has an encoder that has a counter for a number of frames I want it to encode before it stops. The easiest way to adjust that counter would be to use a procedure.