Function fromMat4

fromMat4<T>(m4, dst?): T
Creates a Mat3 from the upper left 3x3 part of a Mat4
Type Parameters
- T extends BaseArgType = number[]
Parameters
- m4: BaseArgType
  source matrix
- Optional dst: T
  matrix to hold result. If not passed a new one is created.
Returns T
Mat3 made from m4