Support Transform to PackedFloatArray conversion

[eSavag]

It would be very useful to more easily map the structure of any given transform to the PackedFloatArray structure used in multimesh buffer.

Because the PackedFloatArray expects the origin values and basis to be intersposed with each other, taking the transform apart requires many different operations/lines of code. The solution would be a method which takes a transform and returns a PackedFloatArray of the right size, with optional parameters allowing for the non-default packedarray sizes, to support customdata etc.

I'm working on a project where I need to update the positions of thousands of multimesh instances on any given physics tick, but the cost of assembling the PackedFloatArrays greatly outweighs the benefit of being able to use the multimesh set buffer command, even though it's supposed to be the more optimised/hot pathway. With my current implementation, using packedfloatarrays and set_buffer results in 5-7 FPS, whereas individually setting the transforms gives me 100-130fps.