Cleanup pass over UniformCTypeMapper::Get.
Cleanup pass over UniformCTypeMapper::Get.

This function was inadvertently making a copy of the supported-type list
immediately before iterating over it. This was harmless but is a
significant amount of unnecessary work. (Fortunately it only occurs at
skslc time, so the performance hit was not user-facing.)

Since I was cleaning up the code anyway, converted search loops to use
range-based `for`.

Change-Id: I20727ea8dd19373db14fcd5d29ebe5a22b85b532
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/400378
Auto-Submit: John Stiles <f4fcf42d3bb5924557f1eeb3be66747535e585da@google.com>
Commit-Queue: John Stiles <f4fcf42d3bb5924557f1eeb3be66747535e585da@google.com>
Reviewed-by: Michael Ludwig <cb1f3dd24de0f0b611b26bc28bec758a551d9b7d@google.com>

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