v126.0 beta8 Release

No user-visible change between m125 and m126
(SkCanvas::drawArc overloaded; Not adding SkArc class yet)

New to m125:

• Metal-enabled on Mac OS, and added Metal APIs equivalents to Vulkan's.

Changes since m124:

• Dropping Python 3.7 support

• GrContext_Base.defaultBackendFormat and GrContext_Base.compressedBackendFormat
  re-enabled (disabled between m87 and m116)

• Corrected two typos in Vulkan code

• MemoryStream.asData and MemoryStream.skipToAlign4 now emulated
  (changed/removed upstream)

What's Changed

• M126 public by @HinTak in #248
• M125 public by @HinTak in #244

Full Changelog: v124.0b7...v126.0b8