A lot of arrays in VertexProgram and PixelProgram have fixed sizes,
so programs that have more nested loops or ifs or deeper call stacks
can cause OOB accesses, which causes security issues in Chromium.

Index clamping was added to prevent any OOB memory accesses here.

This could eventually be fixed properly by first verifying these sizes
and giving shader compile errors when these limits are exceeded.

Bug chromium:915197 chromium:915206 chromium:915218 b/116373662

Change-Id: I2d0710ed0ce6585f139cba49d5b5d8c909ae6391
Reviewed-on: https://swiftshader-review.googlesource.com/c/23568Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Corentin Wallez <cwallez@google.com>