Implement BMesh Operator string enumerators and docs generation.

Partial implementation of T56496 for review.

Reviewers: campbellbarton

Reviewed By: campbellbarton

Differential Revision: https://developer.blender.org/D3635

Python: Cleanup Noise Module

Implements the changes detailed in T56281

Reviewers: campbellbarton

Reviewed By: campbellbarton

Differential Revision: https://developer.blender.org/D3590

Transform: factor out matrix multiply w/ snapping

Fix BMesh edge_bisect, edge_percent being ignored

Also fix float/int/bool access methods

Python: Add support for @ infix operator matrix multiplication

This differential revision implements the code for T56276

Reviewers: campbellbarton

Reviewed By: campbellbarton

Differential Revision: https://developer.blender.org/D3587

Math Lib: varied size vector multiply

Needed for Python mathutils elementwise multiply.

PyAPI: Make skin modifier roots settable

This make the root flag writable using the Python API, using the
generic skin vertex flag setter function.

Reviewed By: Campbell Barton

Differential Revision: https://developer.blender.org/D3583

Expose MVertSkin customdata layer in Python. This allows scripts to change parameters which are used by the skin modifier (such as radius)

Fix for customdata layer copying. Issue was caused by mixing up of destination and source in copy function. Also fixed an error in Py API, check to see if layers were different should be check to see if they're the same.

BMesh Py API Fix: hide attribute of BMesh elements was returning the select flag. Fixed for all elements including loops, although this is commented out anyway. Reported by Crouch in IRC.