Calculate texture clamping X/Y coordinates in parallel.
Calculate texture clamping X/Y coordinates in parallel.

The X and Y values of `clampedCoord` were being calculated and stored
separately, even in cases where work could easily be done in tandem.
Updated the code so that we use .xy when it makes sense to do so.

This CL is a partial re-attempt of http://review.skia.org/318436 but
changing only one variable instead of three.

Change-Id: I8cab3c2225e1d95bc77371f85d46ab45a184e145
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/321116
Commit-Queue: John Stiles <f4fcf42d3bb5924557f1eeb3be66747535e585da@google.com>
Commit-Queue: Brian Salomon <61fabaaf0876044aeedfd8e351e485c028d69e7b@google.com>
Auto-Submit: John Stiles <f4fcf42d3bb5924557f1eeb3be66747535e585da@google.com>
Reviewed-by: Brian Salomon <61fabaaf0876044aeedfd8e351e485c028d69e7b@google.com>

google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,google/skia,google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia