update references to engine.scratch.. functions

[ronso0]

While fixing mixxxdj/mixxx#14000 for me I noticed the scratch controls documentation is incomplete.

Completes the engine scratch function names and adds links to https://github.com/mixxxdj/mixxx/wiki/midi%20scripting#scratching-and-jog-wheels

Furthermore I'd like to clarify if/why the engine.scratch.. functions should be preferred over engine.setValue(group, "scratch2...
For example engine.scratchTick(deck, ticks) vs. engine.setValue(group, "scratch2", speed).
Will start a thread on Zulip soonish.

[JoergAtGithub]

We've also the typescript docu: https://github.com/mixxxdj/mixxx/blob/2704380577e49e80509d3ffaa710ccd279b7166b/res/controllers/engine-api.d.ts#L206-L242

[ronso0]

Okay, what are you proposing?

IIUC engine-api.d.ts is only discoverable when you use a js IDE. Shall we mention it in https://github.com/mixxxdj/mixxx/wiki/midi%20scripting ?

[JoergAtGithub]

I just referenced, as we have already this reviewed documentation text.
A mention of the .ts file in the manual would be helpful too.
BTW: I originally proposed to render the formal API docu into the manual as shown in this POC: https://github.com/mixxxdj/manual/blob/581e6b9ddcb3e7643a1c93864abceac33f617fc2/source/chapters/controller_api/modules/engine_api.engine.md#scratchenable

[ronso0]

Ah okay, I vaguely remember that!

Do you think I should add a loink to all controls I touched here?
Otherwise a separate PR would be better IMO.