Add logic to compute the size and offsets of interface blocks stored in shared (packed) and standard layouts.

The shared layout follows the standard HLSL packing rules for optimal shader performance.

TRAC #22930

Signed-off-by: Nicolas Capens
Signed-off-by: Geoff Lang
Author: Jamie Madill

git-svn-id: https://angleproject.googlecode.com/svn/branches/es3proto@2343 736b8ea6-26fd-11df-bfd4-992fa37f6226