M126 public

[HinTak]

There is no change other than moving skia forward. (Overloading SkCanvas::drawArc was included in the m125 pull since it is harmless).

[HinTak]

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)

@kyamagu there is no user-visible change between m125 and m126, so I thought a 126 beta might as well go out, instead of a 125 beta.

[HinTak]

This differs from #244 by only the additions of release notes and a comment. (Plus change in skia and versioning)

[kyamagu]

Thanks, LGTM

[HinTak]

2091 passed, 98 skipped, 11 xfailed, 27 warnings