some cleanups for halfplanes
some cleanups for halfplanes

Plan is to next move the clipper into utils / SkCanvas itself

Change-Id: Ia79c5bc2750a3a2719f901d255890a8c43ef1b42
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/257916
Reviewed-by: Mike Reed <f5cabf8735907151a446812c9875d6c0c712d847@google.com>
Commit-Queue: Mike Reed <f5cabf8735907151a446812c9875d6c0c712d847@google.com>

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