Perform coordinate clamping on border addressing mode.

Perform coordinate clamping on border addressing mode.

The border addressing mode should ideally blend with the border color
when using linear filtering. Until we have a border of pixels around
2D textures, we should probably avoid bleeding pixels from the opposite
edge and just clamp the coordinates.

Change-Id: I7afbb629998732b62413e00ba7bcd55340c7b9bb
Reviewed-on: https://swiftshader-review.googlesource.com/14289
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>