### Context:
DDC modules are abstractions over how libraries are loaded/updated. The entirety of google3 uses the DDC/legacy module system due to its flexibility extensibility over the other two (ES6 and AMD/RequireJS). Unifying DDC's module system saves us from duplicating work and will allow us to have finer grained control over how JS modules are loaded. This is a a prerequisite to features such as hot reload.
### Overview:
This change plumbs a boolean flag through flutter_tools that switches between DDC (new) and AMD (current) modules. This mode is automatically applied when `--extra-front-end-options=--dartdevc-module-format=ddc` is specified alongside `flutter run`. Other important additions include:
* Splitting Flutter artifacts between DDC and AMD modules
* Adding unit tests for the DDC module system
* Additional bootstrapper logic for the DDC module system
We don't expect to see any user-visible behavior or performance differences.
This is dependent on [incoming module system support in DWDS](https://github.com/dart-lang/webdev/pull/2295) and [additional artifacts in the engine](https://github.com/flutter/engine/pull/47783).
This is part of a greater effort to deprecate the AMD module system: https://github.com/dart-lang/sdk/issues/52361
Flutter web uses requireJS in `debug` mode to assemble a DDC-compiled app from a bunch of small files ("modules").
This caused that `canvaskit.js` (and all other modules that used a browserify-like loading header) didn't work because they attempted to use the `define` function provided by Flutter's instance of `requireJS` (which kept the defined modules private, rather than as globals on the page, as the users of the JS expected).
A [fix](https://github.com/flutter/engine/pull/27342) was added to `flutter/engine` to trick loaders into *not* using the `requireJS` module loader, but a recent change in the fix's js-interop layer *subtly* changed its JS output on the page (objects went from `undefined` to `null`), causing this:
* https://github.com/flutter/flutter/issues/126131 (and others)
This PR hides a bit of code that is commonly used by module loaders to decide that they may use the `define` function provided by requireJS (so the engine workaround can be removed).
## Next steps
* https://github.com/flutter/engine/pull/42941
## Issues
Partially addresses: https://github.com/flutter/flutter/issues/126131 (and others)
## Tests
* Added a unit test to ensure the `delete` stays
* Manually tested with the Gallery app in `debug` mode with a bunch of user-supplied scripts that currently fail to load.
* Also tested hot restart as suggested by @nshahan
Like Android/iOS, only enable --null-assertions if asked. Previously this was enabled by default for web, but in general this has proved to be too breaking to enable by default.
#61042
Enable null safety asserts for web debug mode. This induces runtime asserts at the boundaries between null safe and non-null safe libraries. Adds integration test that validates assertion error is thrown.
#61042
* 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
