Changed UniformBlockArray so that it stores pointers to
UniformBlock objects and adapted the code. Also reverted
a change that had removed constness from some members of
the UniformBlock class.

Bug 22986647

Change-Id: I677a4b2e92da5849e4387e3802dfdfa36dc6b0a4
Reviewed-on: https://swiftshader-review.googlesource.com/3830Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>