Fixes https://github.com/flutter/flutter/issues/15731

This is a workaround for https://github.com/flutter/flutter/issues/15702

Skia was not drawing the paragraph's text blobs in some cases when a
save/restore sequence is done around the canvas->translate call.  The
problem does not occur if an offsetting call to translate is made instead
of the save/restore.  Will need to work with Skia to find the root cause.

Includes the following changes
- Flip analyzer and server to preview-dart-2 by default
- [vm] Move writing snapshot magic value from embedder to VM
- Fix bug in BigInt.from with certain double value
- [vm] Clean up any remaining API scopes in Dart_ShutdownIsolate.
- [analyzer] Don't expect type arguments for class type parameters of static methods.

* pass shadow_color from dart:ui to physical layer

* default shadow color to SK_ColorBLACK

* add doc comments to pushPhysicalShape

This reverts commit 1348ab5b.

As of ba67d0fe, depth/stencil buffer
attachments are never used. This patch eliminates generation and binding
of depth/stencil render buffers since these code paths are no longer hit.

This reverts commit c24e2850.

Previously iOS render buffer storage width and height were not cached if
not using a depth/stencil buffer. This adds a similar check for
colorBuffer to avoid reallocating render buffer storage.

maxIntrinsicWidth should reflect what the width of the text would be if no
soft line breaks are added.  Hard line breaks should still be incorporated
into the maxIntrinsicWidth.

Fixes https://github.com/flutter/flutter/issues/15588

Includes the following changes
- Support for MultiRootFileSystem options in frontend server (will be
  used in google3)

* Roll Dart to version 0175f24b2549732d0010708988fd328440c3f956

Notable runtime changes :

- Translate asserts in the VM-specific async translation

- Fixes flutter code coverage issues

- Fix type test '_Closure class IS FunctionType' in strong mode

- Report a compile-time error on magic const

- Do not skip type checks on closure functions.

- Make Dart_DumpStackTrace work when there is no current isolate.

- [vm/kernel/aot, test tool] Enable global type flow analysis

* updated DEPS

* Update.

* Update new license.

gtest is an old version that predates the googletest and googlemock
merger, all tests should be using the newer googletest that's being
kept in sync with the upstream version.

Update external texture image code to specify GL texture format and image color type rather than GrPixelConfig (#4786)

* Roll Garnet

* Update licenses

This reverts commit d9fcdfb6.