Handle the case of reparenting while updating children

Instead of trying to flush the detached children from the child list, we keep
the set of detached children up to date and query on every read.

show the error codes in flutter analyze --watch

flutter analyze test

AspectRatio should attempt to fit its height

Migrate flutter analyze config to options.

If there's not enough height for the given aspect ratio, we now try to see if
using the height to infer the width will fit the given constraints. The
algorithm we use is similar to the one we use for RenderImage.

Fixes #2620

Update engine

More groundwork to get `analyze` and IDE output to agree.

See: https://github.com/dart-lang/sdk/issues/25723

Test that flutter analyze catches no error if two imported libraries
have the same name.

Also, make tests know how to find the flutter root and fix style in one
test to be consistent with the rest of the file.

Analyze command cleanup.

Run "pub get" if needed in the flutter build command

Add RotatedBox which applies a rotation before layout

Transform applies its transform before painting, but sometimes you want
the widget to layout after its transform has been applied. We can't
handle general tranforms in this way because we can't couple width and
height constriants, but we can handle certain rotations.

Fixes #1214

Remove devicestore

regenerate the i18n files for the stocks example

Removing some special-casing in pursuit of aligning `flutter analyze` output with that provided by server/IDEs.  Specifically:
  * strong-hints (stale, no longer supported)
  * "analyzer says" comment handling in favor of `//ignore`s
  * `conflictingNamePattern` --- no longer needed

Next up some of the error filter regexps...

Markdown is now correctly updated when config changes

Add DevicePortForwarder with adb fix

exclude the i18n files from analysis

Provide the BuildContext to createRenderObject and updateRenderObject

We'll need this for RTL support because the RTL state will live in the widget
tree. Also, remove the `oldWidget` argument to updateRenderObject because there
aren't any clients for it.

api docs: Add descriptions for Scaffold, Theme, and ThemeData classes.

Enable ALL THE LINTS

Well, all the easy ones, anyway.

For some reason `// ignore:` isn't working for me so I've disabled
lints that need that. Also disabled those that require a ton of work
(which I'm doing, but not in this PR, to keep it reviewable).

This adds:
- avoid_init_to_null
- library_names
- package_api_docs
- package_names
- package_prefixed_library_names
- prefer_is_not_empty
- sort_constructors_first
- sort_unnamed_constructors_first
- unnecessary_getters_setters

Remove the _EquationMember.hashCode override

Fix crash when dumping the app if it uses RichText

Specifically:

* Handle null styles in TextSpan without crashing in toString().

* Handle null children in TextSpan child lists without crashing in
  toString().

* Handle entirely empty TextSpans in toString() explicitly.

* Assert that TextSpans don't contain nulls in various places. This is
  done more often than one might think necessary, because it turns out
  that TextSpan takes a (mutable) List for one of its arguments, so
  who knows what it will contain at any given time. By asserting all
  over the place, hopefully we'll catch it near the change if they do
  change it.

* Add a RichText example to Stocks to exercise RichText and TextSpans.

See also: https://github.com/flutter/flutter/issues/2514, https://github.com/flutter/flutter/issues/2519

Prepare to make RenderObjectElement buildable

This patch prepares us to pass a BuildContext to RenderObjectWidgets, which
will make it possible to rebuild RenderObjectElements:

 * Delay creation of the render object until mount(). That will let us pass
   `this` to createRenderObject and have the inherited elements be initialized.

 * Cleanup widgets that take builder closures to prepare for their
   RenderObjectElement to be rebuilt more often.

 * Add a test for the interaction between inherited widgets and
   MixedViewport.

Related to #2598