This PR fixes the dropping of both the `path` and `search` fields from the platform location in the URL when using Flutter Web and brings it in par with similar technologies (e.g. React Router).
It allows developers to keep the original path and/or search parameters in the URL, which are perfectly valid even while fragment routing is present.

**Example use case:**
Call a Flutter Web app with initial config parameters in the URL: 
`http://my-flutter.app/?skipIntro=true`

**Example:**
Before initial routing:
`http://localhost:45389/?foo=bar`
After routing:
`http://localhost:45389/#/menu`
After routing (with fix):
`http://localhost:45389/?foo=bar#menu`

Fixes #116415

This is based off (and dependent on) these changes in the web engine that expose web-specific APIs: https://github.com/flutter/engine/pull/40608

See https://github.com/flutter/flutter/pull/103719

This reverts commit 5fd259be.

This reverts commit d056500b.

This reverts commit 31de052e.

This reverts commit e2490f29.

This reverts commit 35ad43f2.

This reverts commit c26ed03c.

* Migrate to ChannelBuffers.push

* Move TestDefaultBinaryMessenger to its own file

* Apply deprecations and fix usages

This reverts commit 2d9a01a8.

Force opt-in flutter test platform to null safety for repo testing

* Update project.pbxproj files to say Flutter rather than Chromium

Also, the templates now have an empty organization so that we don't cause people to give their apps a Flutter copyright.

* Update the copyright notice checker to require a standard notice on all files

* Update copyrights on Dart files. (This was a mechanical commit.)

* Fix weird license headers on Dart files that deviate from our conventions; relicense Shrine.

Some were already marked "The Flutter Authors", not clear why. Their
dates have been normalized. Some were missing the blank line after the
license. Some were randomly different in trivial ways for no apparent
reason (e.g. missing the trailing period).

* Clean up the copyrights in non-Dart files. (Manual edits.)

Also, make sure templates don't have copyrights.

* Fix some more ORGANIZATIONNAMEs

This reverts commit 13a1b1e3. It broke the build.

fix and enable painting tests on the Web

* Allow sending messages from the platform to the framework

* Add ability to send messages from the plugin to the platform.

Also adds [PluginEventChannel] which is the plugin counterpart to
EventChannel.

Fixes https://github.com/flutter/flutter/issues/39981

* fix analyzer errors

* Enhance doc comments

* Remove dead code in test