`stiffness` is the name of a spring's `k` input on [iOS](https://developer.apple.com/documentation/quartzcore/caspringanimation), [Android](https://developer.android.com/topic/libraries/support-library/preview/spring-animation.html), and the [Web](https://github.com/skevy/wobble/blob/bbc0f831e234f2d24fb905f2ec278c134d69ed68/src/index.js#L11-L22).  To ensure the API is familiar to and easily understood by developers coming from other platforms, Flutter should follow this convention as well.

This is a minimally-breaking change.  Across [all of GitHub](https://github.com/search?l=Dart&q=springConstant&type=Code&utf8=%E2%9C%93), there are only 2 uses of the `springConstant` API (in Mondrian).  Those can be easily changed to use this name.

Closes #11684

* refactor to assembleSemanticNode

* ++

* cleanup

* fix test

* add note

* review comments

* review feedback

* import fix

* another import fix

* refactor to ensure tag

* tests, tests, tests

* analyzer fixes

* review comments

During FLX snapshotting, changes to (or absence of) any of the following
should trigger re-snapshot:

  1. main() entrypoint source
  2. transitive closure of sources reachable from the entrypoint source
  3. the output snapshot

Fixes https://github.com/flutter/flutter/issues/11722

This patch supports basic filtering of log lines from physical iOS
devices, similar to existing functionality for iOS simulator logging.

This patch also suppresses the following two log messages which are
emitted at app startup on iOS 10.3 devices:
  libMobileGestalt MobileGestaltSupport.m:153: pid 123 (Runner) does not have sandbox access for frZQaeyWLUvLjeuEK43hmg and IS NOT appropriately entitled
  libMobileGestalt MobileGestalt.c:550: no access to InverseDeviceID (see <rdar://problem/11744455>)

These properties had a high cost in the documentation because they're
all top-level properties, and there's really very little reason for
these values to be configurable in the first place.

Allows the user to specify the kind of project to create. The default is 'app'. Other choices are 'plugin' (the old '--plugin' behavior), and 'package'.

A Flutter 'package' is a Dart package that depends on Flutter, but does not contain native code.

Fixes #10377.

* Add comments to 3 methods that were missing comments.

Fix out of order (getter, private field, setter) tuple

* Code review fix.

The flakiness of commands_test is generally visible via:

```
drive:stdout:   Expected: 'log: paint'
drive:stdout:     Actual: ''
drive:stdout:      Which: is different. Both strings start the same, but the actual value is missing the following trailing characters: log: paint ...
```

By returning the name of the test we will be able to understand if
another test is running by reading the `Actual` value

This reverts commit 8d07d3f6.

This reverts commit 5f9acc41.

* fix some call sites of printError

* review comments

Bare bones widget inspector support.

Toggle the widget inspector from the flutter tool by pressing 'i'.
When the widget inspector is select mode:
Pointer down to to inspect a widget.
Pointer click to finalize selection of a widget. You can now interact
with the application as you normally would but with the inspected widget
highlighted.
Click the inspect icon in bottom left corner of screen to reactivate
select mode.

Addresses
https://github.com/flutter/flutter/pull/11705/files/3b4687bf69e41bd74db230452b36c0898d01dfa5#r134325222

- Wait for full Hot Reload
- Wait for full Restart
- Fallback if checkHealth throws METHOD_NOT_FOUND.
  We try to wait for the service extensions to be registered and retry.

when describing non-nullable method arguments.

Some widgets are using closures even if the only values that are
captured are this, context or widget, that can be accessed even from
methods of the State object.

This reverts commit 1705bf3c.

* Revert "Fix a typo in the saved certificate error message (#11640)"

This reverts commit bfda885a.

* Revert "Rollback patch that broke microbenchmarks (#11616)"

This reverts commit 70fe6f4c.