Blender Git Loki

Fix T67939: GPencil Noise modifier wrong random calculation

There were several problems in the old random calculation:

* Different result in the viewport and render.
* Noise "pop" in some frames.
* Random number was calculated every time the file was opened, so get different results.

Now, instead to calculate the random numbers when n number of frames changed, the random values are calculated using a unique seed by stroke.

Also, a new Seed parameter has been added and this adds more control in the noise generated. This value can be animated and get more variations.

Differential Revision: https://developer.blender.org/D5393