In case the shader version is greater than ESSL 1.00, the precision
emulation needs to output rounding functions for non-square matrix
types.

Writing emulated compound assignment functions for non-square matrices
already had most of the code in place before this change.

New compound assignment operators like >>= don't need floating point
precision emulation in ESSL 3.00, since all of them only operate on
integers.

BUG=angleproject:1434
TEST=angle_unittests

Change-Id: I4678f511edf4f9f744fe23bb8d7dab4387f07f20
Reviewed-on: https://chromium-review.googlesource.com/358472Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>