Reduce template usage in vector-coalesce functionality.
Reduce template usage in vector-coalesce functionality.

The main loop of vector-coalesce is now a single function that operates
exclusively on double values, rather than being templated on its input
types.

A similar approach should work equally well on evaluate-n-way-intrinsic.

Change-Id: Ic2848b52365ed5e38f6432f881b2ac593668a148
Bug: skia:12233
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/437917
Auto-Submit: John Stiles <f4fcf42d3bb5924557f1eeb3be66747535e585da@google.com>
Commit-Queue: John Stiles <f4fcf42d3bb5924557f1eeb3be66747535e585da@google.com>
Reviewed-by: Brian Osman <794c0b5534edf5601d88e1d41975d0262da12894@google.com>

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