Fixes #18145.

A bug in _RenderCustomClip was compaeing the type of oldClipper to
itself instead to the type of newClipper.

This was the root cause for the crash #14937 worked around.
This also reverts the workaround introduced in #14937.

* Surface border parameter in CupertinoSliverNavigationBar (#18152)

* Add tests for CupertinoSliverNavigationBar border

* Remove unused keys, find by descendant

* Use `cirrusci/windowsservercore:2016` container for CI

with 4 CPUs

* Removed `Dockerfile.windows`

This registers compile-expression service that is used by dart vm to evaluate expressions when debugging flutter applications.

* Document flutter run --machine at the bottom of the doc
* Be consistent with prefixes

Fixes https://github.com/flutter/flutter/issues/14517
Or at least, fixes the crash part of that.

* Documented nested navigators in the Navigator class file (#15040).

This reverts commit 4f1b6604.

Now that we have thousands of tests, it doesn't make sense to display a separate line for each test. The result is just megabytes of logs that you have to scrub through to find error messages.

Fixes #15198.

* TextFormField/TextField - remove spaces in character counter(follow material design guidelines)

The change in 8b8d368d has only renamed the flag in a subset of the
places.

We were already skipping the check in `flutter upgrade` but this also spawns `flutter precache` and `flutter doctor` which would still check and potentially output the message.

Eliminates 64-bit hardcoding for iOS test apps under dev/. This brings
them in line with the default iOS app templates.