Update docs to reflect Registering MIDI Input Handlers From Javascript feature

[christophehenry]

Bug Description

Since #12781 MIDI input handlers can be registered from Javascript. Components-JS page should be edited to document this change and the feature spec page should be removed

Version

all

OS

all

[Swiftb0y]

Since this feature is currently not integrated in componentsJS we should just add it to MIDI Scripting. #13437 presents an opportunity to do that integration.