This fixes issues 11940 and 18155.

* enable lint unnecessary_new

* fix tests

* fix tests

* fix tests

* Fixes resulting from audit of issues links

I looked at every link to GitHub in our repo. For cases where we had a TODO that was waiting for a bug to be fixed, and the bug has now been fixed, I applied the pending change. For cases where the link was out of date, I updated the link.

* Update run_test.dart

skip this test again since it failed on linux and macos bots

* adjust declared types to work with dart 2 typing at runtime

* review comments

* update packages/flutter_tools/lib/src/ios/simulators.dart

This makes it easier to run ios add2app apps with Flutter run.

This updates AppContext per the recommendations in #15352

Fixes #15352

* Revert "Revert "Add android license verification to doctor and some refactoring" (#14727)"

This reverts commit d2602947.

* Add tests, fix sdkManagerEnv and use it consistently, and rearrange Status object model

* AnsiSpinner needs to leave the cursor where it found it.

* fix tests

* Const constructor warning only shows up on windows...?

* Avoid crash if we can't find the home directory

* Make pathVarSeparator return a string in the mock

* Implement review comments

* Fix out-of-order problem on stop

* add a --machine mode to flutter config

* review feedback

* add min version checks for IntelliJ

* validate the installed versions of IntelliJ and the flutter plugin

* review comments

Fixes https://github.com/flutter/flutter/issues/9929

Fixes #9866

Old Android Stuio versions pior to 2.2.0 didn't come with Java bundled. Make sure flutter doesn't crash when we try to determine the Java version of those old Android Studio installations.

* Use Java bundled with Android Studio for gradle

* review comments

Fixes #8395.

It's not just $HOME/.AndroidStudio2.2, it might also be
.AndroidStudioPreview2.3, or .AndroidStudioFooBar1.7, or whatever.

Made the Version parser less throw-happy, and relaxed the directory name
checks to allow for the above.

Fixes #8353.

* Fix bug parsing Gradle version.

Version from pub_semver requires versions of the format X.Y.Z. Gradle
doesn't follow semantic versioning, though, so version parsing would
fail on versions like '3.2'. Fixed by writing a custom Version class.

Also removed a check for apksigner when building Gradle-based projects.

Fixes #8298

Finally found the command to run tests in checked mode on my system. This one should've been caught by the IDE, but wasn't.

* Teach flutter tools to find gradle

Flutter tools will now use Gradle from Android Studio, which is now found automatically.

flutter doctor will verify that Android Studio has been installed, and that the included Gradle is at least version 2.14.1.

It is still possible to manually configure the path to Android Studio (flutter config --android-studio-dir=XXX) or Gradle (flutter config --gradle-dir=XXX), but this should only be necessary if they're installed somewhere non-standard.

Only tested on Linux and macOS for now.

Fixes #8131