free skvx from its Skia shackles
free skvx from its Skia shackles

Remove the need to include SkTypes.h in SkVx.h,
making SkVx entirely independent of Skia.

As an experiment, switch to checking Clang/GCC-style __SSE__ /
__ARM_NEON defines directly instead of the slightly more abstract
SK_CPU_SSE_LEVEL / SK_ARM_HAS_NEON.

Those SK_ defines only exist to help SSE detection on MSVC, which SkVx
generates serial code for anyway.

If this sticks I may do this same sort of change all through Skia.

Change-Id: I1c51fd6ba1fa48f199ce623824d5ef20ff6be995
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/219541
Reviewed-by: Brian Osman <794c0b5534edf5601d88e1d41975d0262da12894@google.com>
Reviewed-by: Michael Ludwig <cb1f3dd24de0f0b611b26bc28bec758a551d9b7d@google.com>
Commit-Queue: Mike Klein <14574f09dfa9b4e14759b88c3426a495a0e627b0@google.com>

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