Reland "Delete GN support for building for fuchsia"

This reverts commit 3539a4ea51922728f4ba06fb5ea9d8af45849e8f.

Reason for revert: Fixed upstream

Client CLs:
 - https://github.com/flutter/flutter/pull/171800
 - https://github.com/flutter/flutter/pull/171874
 - https://github.com/flutter/flutter/pull/172104

Bug: b/427681157
Original change's description:
> Revert "Delete GN support for building for fuchsia"
>
> This reverts commit b6e7fee4ae9b9108da8264f24a3dd04462b912ed.
>
> Reason for revert: Breaking Fuchsia tests
>
> Bug: b/427681157
> Original change's description:
> > Delete GN support for building for fuchsia
> >
> > This mostly was added in [1] for building SkQP for Fuchsia.
> > There are no automated CI tests that build for Fuchsia in
> > the Skia suite and I am not aware of any dev building these
> > locally. Thus, I'm declaring these things unused.
> >
> > This CL *does not* delete SkFontMgr_fuchsia.cpp, which is
> > used in chromium (e.g. [2]) which has its own GN rules for
> > building Skia for Fuchsia [3]. Skia's ports.gni file still
> > lists those files [4] so clients can use them in their own GN build.
> >
> > If this breaks things, it'll be illuminating and unexpected.
> >
> > [1] https://skia-review.googlesource.com/c/skia/+/244369
> > [2] https://source.chromium.org/chromium/chromium/src/+/main:skia/ext/fontmgr_fuchsia_unittest.cc;l=20;drc=f6492524f906d0728ddd5d41daf071f4b89300ba;bpv=1;bpt=1
> > [3] https://source.chromium.org/chromium/chromium/src/+/main:skia/BUILD.gn;l=469-484;bpv=1;bpt=0
> > [4] https://github.com/google/skia/blob/ef104904659ff58bca9e3332606009c26c7b5540/gn/ports.gni#L112-L116
> >
> > Bug: b/427681157
> > Change-Id: I2f855c9c875a1844422178999958442be8dcb035
> > Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1017296
> > Commit-Queue: Kaylee Lubick <kjlubick@google.com>
> > Auto-Submit: Kaylee Lubick <kjlubick@google.com>
> > Reviewed-by: Thomas Smith <thomsmit@google.com>
>
> Bug: b/427681157
> Change-Id: If4caf816db8e69c71ebd362fedbe8e9a39ddae48
> No-Try: true
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1018617
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Reviewed-by: Thomas Smith <thomsmit@google.com>

Bug: b/427681157
Change-Id: I6485b6404f9e573ac87f5bbdb64cf2060ffebb9c
No-Try: true
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1019617
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Thomas Smith <thomsmit@google.com>
21 files changed