Fixes #4166.
Fixes #5120.
Fixes #5399.
Fixes #6507.

Required for compatibility with older versions of Android

* refactor _run to runCmd

* replace requiresProjectRoot getter with call to commandValidator

* replace requiresDevice getter with call to findTargetDevice

* trace command requires a debug connection, not a device

* inline androidOnly getter

* rename command methods to verifyTheRunCmd and runCmd

* move common verification into BuildSubCommand

* rename deviceForCommand to device

* rename methods to verifyThenRunCommand and runCommand

Fixes https://github.com/flutter/flutter/issues/5592

This change adds a top-level getBuildDirectory func and funcs for
android, aot, asset, ios build products.

Developers may now add a "build-dir" mapping to their
~/.flutter_settings (JSON format) config file. Output directory is
relative to the main flutter application directory.

This change also changes the default build directory for iOS builds to a
subdirectory of the configured build directory, 'build/ios' by default.

* This reverts commit 5e7e7b6e.

* default to lib/main.dart

This reverts commit 32ad81c8.

* making flutter run work with gradle

* locate android studio

* add test for settings

* review comments

The new `empty_statements` lint (in the next DEV roll), flags these empty statements.  Harmless, except the one in `basic.dart` that fixes a real-life bug. :)

See https://github.com/flutter/flutter/issues/4438

* refactor the --resident run option into a separate file

* update daemon to run --resident apps

* re-plumbing daemon start

* send app logs

* update tests

* review changes

* fix test runner

* remove PackageMap.createGlobalInstance; rely on the ctor

* review comments

* show build progress; print app sizes

* add todo

* review comments

* remove unused import

On iOS, we use Xcode to build a static library that contains the precompiled
code. This code is currently unused, but it will be used by the new Xcode
harness to factor out as much complexity as possible into the flutter tool.

* rebuild when the build type changes

* handle local engine builds

* also check the timestamp

This also fixes some related problems affecting "flutter run":
  * FLXes built during AndroidDevice.startApp need to match the build mode
  * APKs should always be rebuilt if the build mode uses AOT compilation

Artifacts from local engine builds will be found based on the --local-engine flag

Host tools can be found in the artifact cache directory for the host platform.
If a developer wants to use a local engine build instead, then provide an
--engine-build flag that selects the specific engine build variant.

* complain on missing entries in flutter.yaml

* change to a hard failure

* fix analysis errors

* review comments; fix test

* re-add an export for debugPrint

Also update the engine to a build where these tools have been uplaoded

Fixes #3624

This currently requires a local build of the engine.

Run "flutter build aot" to build an AOT snapshot.
Run "flutter build apk --profile" to build a "profile mode" APK that uses AOT.

* rename the --develop option to --debug

* fail if both --debug and --deploy are specified

* download android-arm-deploy

* wire up --deploy to android-arm-deploy

* fix interpolation

* add a --deploy flag to build apk

* update command description

* use an enum instead of a bool param for build variants

* rename buildForDeploy flag to buildVariant

* review comments

* add a target for android-x64

* update armeabi-v7a to x86_64