The line raster emulation coded uses round() which was previously not
translated.  This change implements all operations supported by
TIntermUnary nodes.  Bresenham line emulation is now allowed.

Bug: angleproject:4889
Change-Id: I1ffbe3f9bf0299f7efa2c6d1e8f011fefdbb2ddb
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2951624
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Tim Van Patten <timvp@google.com>