* Only printError on our simple messages

Any other type is a real error that should be a normal crash (to get a proper error log).

See #19453.

* Add toList() to convert Iterable<String> -> List<String>

This code previously throw in Dart-2 mode.

Fixes #19453.

* Move getSimulatorPath into Xcode

* Add a test that we tried to launch the simulator

* Remove unused import

* Add --create option to flutter emulators

* Tweaks to error message

* Simplify emulator search logic

* Make name optional

* Add a note about this option being used with --create

* Tweaks to help information

* Switch to processManager for easier testing

* Don't crash on missing files or missing properties in Android Emulator

* Move name suffixing into emulator manager

This allows it to be tested in the EmulatorManager tests and also used by daemon later if desired.

* Pass the context's android SDK through so it can be mocked by tests

* Misc fixes

* Add tests around emulator creation

Process calls are mocked to avoid needing a real SDK (and to be fast). Full integration tests may be useful, but may require ensuring all build environments etc. are set up correctly.

* Simplify avdManagerPath

Previous changes were to emulatorPath!

* Fix lint errors

* Fix incorrect file exgtension for Windows

* Fix an issue where no system images would crash

reduce throws on an empty collection.

* Fix "null" appearing in error messages

The name we attempted to use will now always be returned, even in the case of failure.

* Add additional info to missing-system-image failure message

On Windows after installing Andriod Studio I didn't have any of these and got this message. Installing with sdkmanager fixed the issue.

* Fix thrown errors

runResult had a toString() but we moved to ProcessResult when switching to ProcessManager to this ended up throwing "Instance of ProcessResult".

* Fix package import

* Fix more package imports

* Move mock implementation into Mock class

There seemed to be issues using Lists in args with Mockito that I couldn't figure out (docs say to use typed() but I couldn't make this compile with these lists still)..

* Rename method that's ambigious now we have create

* Handle where there's no avd path

* Add another toList() :(

* Remove comment that was rewritten

* Fix forbidden import

* Make optional arg more obviously optional

* Reformat doc

* Note that we create a pixel device in help text

* Make this a named arg

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

`flutter emulators nexus` will now return only those that'd match (eg. same things that `flutter emulators --start nexus` would match).

And it's not obvious to the use what the ID is.

Very basic support for "flutter emulators" which just lists the available Android AVDs.

Relates to:

https://github.com/flutter/flutter/issues/14822
https://github.com/Dart-Code/Dart-Code/issues/490
https://github.com/flutter/flutter/issues/13379