Fixes #11868

Fixes #11848

Also, fix the interpolation between visual and directional fractional
offsets. The interpolation now works visually in whatever direction the
result eventually gets resolved into.

Fixes #11847
Fixes #11357

* Fixed TrackingScrollController cleaning stored offset on position's detach

* Fixed format.

* Fixed format.

* Fixed test with Directionality support.

Fixes #11379

Fix a test for build invalidation due to a change in main entry point.
Previously this test's build was always invalidated to the the lack of a
previous snapshot (as well as the change in checksums). This change
ensures that the build is invalidated only due to the change in
checksums.

Most of the framework widgets should work in terms of EdgeInsetsGeometry
rather than EdgeInsets so that their clients can supply directional
insets.

* enable lint prefer_final_fields

* enable lint recursive_getters

* enable lint unnecessary_overrides

Fixes #5215

Fixes #11381

This reverts commit ec25f6bd.

* Fixed TrackingScrollController cleaning stored offset on position's detach

* Fixed format.

* Fixed format.

extract_messages script currently fails to parse this file because of its use of static asserts, super and a ctr body. Since we already have an assert in the body, I think it is also more readable to put all of them together. _LocalizationScope follows the same pattern above.

This patch migrates iOS device listing from using Xcode instruments to
using the libimobiledevice tools idevice_id and ideviceinfo.

ideviceinfo was previously incompatible with iOS 11 physical devices;
this has now been fixed.

In 37bb5f13 flutter_tools migrated from
libimobiledevice-based device listing on iOS to using Xcode instruments
to work around the lack of support for iOS 11. Using instruments entails
several downsides, including a significantly higher performance hit, and
leaking hung DTServiceHub processes in certain cases when a simulator is
running, necessitating workarounds in which we watched for, and cleaned
up leaked DTServiceHub processes. This patch returns reverts the move to
instruments now that it's no longer necessary.

* rename Element.visitChildrenForSemantics to debugVisitOnstageChildren

* address comments

* Improve the Flex overflow marker style

* Update basic.dart

* Update Hot Reload label text in template app instructions.

* label fix

This adds --preview-dart-2 flag that enables use of Dart 2.0 Frontend in Flutter tools.

* Revert "Revert "fire service protocol events for frames (#11565)" (#11727)"

This reverts commit f25e2f52.

* move the postEvent() call into a separate method

Fixes #11373

This patch includes:

 * SliverPadding
 * ScrollView
 * PageView

Fixes #11764
Fixes #11836

* fix typo in State.didUpdateWidget

* rephrase