improve/clone PositionScratchController for use with controller mappings

[ronso0]

Feature Description

The benefit over engine.scratchTick() and scratch2:

• no drift
• built-in inertia mode (backspins, throws)
• slow scratching with PositionScratchController can sound much smoother

(When comparing these methods make sure to use high-res tracks so that track artifacts are not mistaken for scratch artifacts!)

Actually it does already work quite nicely with the existing controls scratch_position_enable and scratch_position.
The latter requires an absolute position (like those sent by the S3/S4 Mk3 wheels) with factor X to achieve the desired scratch speed, though that can be emulated with relative psoitions, too: the mapping can accumulate ticks on wheel touch and send its internal 'absolute' position.
See #14004

IIUC the main difference (reason for drift) is that engine.scratchTick() and scratch2 compute ticks/scratch rate in between engine process calls, so the engine inevitably misses 'position' updates. Maybe engine.scratchTick() can also be optimized but I found it much easier to work with the existing PositionScratchController implementation.
And scratch2 / engine.scratchTick() (using scratch2) can apparently easily overshoot when scratching slowly.

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PositionScratchController is built for mouse scratching, so for optimum controller performance it would be nice to have controls/parameters to adjust the sample period and probably other parameters.
For a starter I suggest to clone PositionScratchController --> WheelScratchCotroller so its settings don't affect the waveforms scratching.

What do you think?