Requests: Add ToggleSceneItemEnabled

[theca11]

Description

Adds a new request called ToggleSceneItemEnabled which toggles the enable state of a scene item and returns the new state.

Motivation and Context

Closes #1153

How Has This Been Tested?

Tested OS(s): Windows 10 (22H2 19045)
New request tested with the help of obs-websocket-js lib:

1. Fetch sceneItemId value with GetSceneItemId
2. const {sceneItemEnabled} = obs.call('ToggleSceneItemEnabled', {sceneName: 'My scene', sceneItemId: 1234});

Types of changes

• New request/event
• Documentation change (a change to documentation pages)

Checklist:

• I have read the Contributing Guidelines.
• All commit messages are properly formatted and commits squashed where appropriate.
• My code is not on master or a release/* branch.
• The code has been tested.
• I have included updates to all appropriate documentation.