Previously, the only hook into the rasterizer schreenshot code path
was via FlutterDriver.screenshot.  This adds the ability for the
Flutter tool to hook into all three types of screenshots:

1. device (e.g. `adb shell screencap`)
2. Skia (capture spk)
3. Rasterizer (capture PNG via the engine)

This contains the following commits:

flutter/engine@fade83c Bypass the raster cache when screenshotting

Before this change, if you specified a non-null textTheme, but the theme you specified didn't have a body2 defined, then creating a ChipTheme would assert (which means creating a ThemeData would fail).

This adds handling for this corner case to default to reasonable values in that case. The slider had the same problem, but for accentTextTheme, so I fixed that too.

While I had the patient open, Hans and I noticed that TextTheme.merge wasn't doing the right thing in the case where some members were null either, so I fixed that, and added some examples, since merge/copyWith are common operations that are not always well understood.

Fixes #17251

* no longer use the analyzer version shipped in the sdk

* update all package versions to the latest

This reverts #17147, which was safe under the assumption that
getArtifactPath() returns a platform-specific gen_snapshot instance
(which have the correct default set for this flag) -- it turns out that
though we pass the platform to getArtifactPath(), we always return the
host gen_snapshot for Android.

A followup patch will update getArtifactPath and revert this patch.

re-write flutter analyze (the single-shot and --flutter-repo) to use the analysis server

We've always cached kernel compiles during bundle builds. This adds
caching for kernel compiles during AOT builds by moving caching into the
KernelCompiler.compile() method rather than around each invocation of it.

This also filters buildbot paths included by the kernel compile that are
not present on the local machine at paths /b/build/slave/Linux_Engine/...
The kernel compiler should probably include an option to not emit these
paths in the depfile, since these are used both by Gradle and the
Fingerprinter class.

Previously, Flutter did not support iOS devices with armv7 or armv7s
CPUs. We now support these devices. This eliminates the previous
hardcoded checks that prevented running on simulators of older devices.

We maintain the existing restriction on running on watchOS or tvOS
simulators.

Previously, in non-release (i.e. profile) AOT builds, we were setting
--no-checked and --conditional_directives flags. --no-checked is the
default, and we don't make use of conditional directives in Flutter.

Allows users of Fingerprinter to filter the set of paths collected from
the explicitly-specified paths and those collected from depfiles.

In some cases, depfiles are emitted with files that are not present on
the local disk (e.g. the frontend compiler currently emits buildbot
paths for the dart core libraries and dart:ui). These files will not
materially affect whether we need to re-run a build action for which
they are inputs, since they're not present in the filesystem and
therefore cannot change.

Fixes https://github.com/flutter/flutter/issues/16169

Depending on whether can read the AVD (or it even has all fields populated) we might get extra "empty" columns, so this trims all blank cells from the end.

It feels more nautral to type when doing `--launch x` or `--create x`.

Emaultor keeps running on a seuccessful launch, so this automatically returns after 3 seconds if the process hasn't quit (we have to wait for some period to get stderr in the case of a failure).

I can't come up with a better name; anything with Simulator or Device in it will be confused with the existing IOSSimulator/Device classes (which represent the running devices).