* Add Windows unit tests to plugin template

Adds an example native unit test to the plugin template for Windows,
matching the format we use for our 1P plugin example app unit tests.
Once these have been added for all platforms+languages, they will be
documented on a new plugin development page to explain their use.

Since we don't appear to be running our current plugin e2e tests for
Windows, this adds a new configuration to run them. I haven't
`led`-tested this, so it may not work, but this will give a starting
point for getting them running.

Part of https://github.com/flutter/flutter/issues/82458

* Minor fix

* Add test owner

* Fix typo

* Fix test feature flag

* Improve Swift plugin implementation

* Add iOS tests

* Review feedback on structure

* Remove duplicate scheme file

* Add macOS

* Add iOS

* swift test tweaks

* unit tests

* Whitespace

* Add e2e tests

* Remove trailing spaces

* more

* empty commit

This reverts commit 5257f029.

* Building shared C source code as part of the native build for platforms Android, iOS, Linux desktop, MacOS desktop, and Windows desktop.
* Sample code doing a synchronous FFI call.
* Sample code doing a long running synchronous FFI call on a helper isolate.
* Use of `package:ffigen` to generate the bindings.

This reverts commit 9038fac9.

This reverts commit 058dfd49.

* Revert "Mark last failing test after gradle update as flaky. (#91423)"

This reverts commit 46a52d03.

* Revert "fix android template for Gradle 7 (#91411)"

This reverts commit 51d06d53.

* Revert "Add explicit version for mac and windows openjdk. (#91408)"

This reverts commit bf429f27.

* Revert "Update the openjdk version used by linux android tests. (#91405)"

This reverts commit 2144ab8b.

* Revert "Migrate to Gradle 7.0.2 / AGP 7.0.1 (#90642)"

This reverts commit b6459f9b.

When we landed the CMake minimum requirement constraint for Visual
Studio 2019, we landed it with minimum version 3.15, since that's what
was shipping with the current version of VS 2019 at the time. Looking at
the release notes of earlier versions, it's clear that earlier versions
of Visual Studio 2019 shipped with version 3.14. See:
https://devblogs.microsoft.com/cppblog/visual-studio-cmake-support-clang-llvm-cmake-3-14-vcpkg-and-performance-improvements/

Looking at release notes for CMake 3.15, there are no features/fixes
introduced in that version that we are dependent on.
https://cmake.org/cmake/help/latest/release/3.15.html

Issue: https://github.com/flutter/flutter/issues/88589

* Update .gitignore.tmpl

* Add pubspec.lock

* Exclude example/pubspec.lock

* Address feedback

Signed-off-by: Sunbreak <sunbreak.wang@gmail.com>

In principle this is backwards compatible; I just merged all the classes into one and deprecated everything that became redundant as a result.

[flutter_tools] Display "no platforms" message based on results when creating plugins project (#70215)

This reverts commit 8e73bab9.