* Search for a suitable ARM sysroot instead of hardcoding it;
* Add facility to explain why NDK was not found;

This contains the following commits:

flutter/engine@9ae10ef Revert f6359e4111d37652409e2392fdb3cb72f1119c2a

This contains the following commits:

flutter/engine@b856303 Revert 37e20af6a324cd4cfa1324b8c644712ef8224359
flutter/engine@39c02c4 Fixed Windows build after Blink removal
flutter/engine@4a4cff9 Remove Blink code
flutter/engine@f2acd0a Roll src/third_party/skia/ f31fece65..1d686a962 (10 commits)

Adds unit tests for the following AOT build configurations:
* iOS armv7 profile
* iOS armv7 release
* Android armv7 profile (AOT blob)
* Android arm64 profile (AOT blob)
* Android armv7 release (AOT blob)
* Android arm64 release (AOT blob)

Further digging revealed that the reason --no-sim-use-hardfp was
required to be specified explicitly was that Android engine gen_snapshot
binaries are built on Windows with target_os=win.

This fixes #17169 by adding onChangeStart and onChangeEnd to the slider. These will be called when the user starts a change, and when they end a change, regardless of whether that change is a tap or a drag.

These differ from onChanged, in that they only report when the user starts and ends an interaction, not at every slight change.

The non-deprecated variants aren't widely available yet

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.