Fix typechecking on matrix-vector multiplications

[davepagurek]

These should be allowed

[pbardea]

Do we also want to allow vector + matrix addition/subtraction/division?

I think they all will make sense but my lin-alg is a bit rusty.

[davepagurek]

For addition and subtraction, it's elementwise, so it has to be the same size. For multiplication, the width of the left hand side must equal the height of the right hand side.

[pbardea]

For now, probably makes sense to just trust the user. When we want to add this type of type-checking, we'll add it in w/ the rest of the type checking which will be done as a walk through the AST after it's been constructed.

[davepagurek]

https://en.wikibooks.org/wiki/GLSL_Programming/Vector_and_Matrix_Operations#Operators for reference on what's defined and what the result is