Ported Angle's std140 encoder to SwiftShader

Ported Angle's std140 encoder to SwiftShader

Added Angle's std140 encoder to properly compute sizes and
offsets of uniform blocks for the std140 standard. All
layouts currently use std140 ('packed' and 'shared' are
implementation dependent, so we can choose to have them be
the same as std140).

All uniform blocks made of simple types or arrays of simple
types are properly interpreted by this code.

Structs are still TBD.

Change-Id: I191d7f313db5d409715b1101ea70903a7b958726
Reviewed-on: https://swiftshader-review.googlesource.com/4525
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>