Use `package:web` and `dart:js_interop` instead.

Part of https://github.com/flutter/flutter/issues/127030

dart:js_interop and package:js will start conflicting, since they both have an `@JS` annotation. Until we're ready to only use dart:js_interop (which will require updating the SDK constraints of every package), we should hide the `@JS` annotation from dart:js_interop. Due to shadowing, this is the behavior today, so there should be no functional change.

Unblocks https://dart-review.googlesource.com/c/sdk/+/294130/8 and prevents confusing shadowing of dart:js_interop annotations like we do today.

- [Mentioned CL that is unblocked] I listed at least one issue that this PR fixes in the description above.
- [Need test-exemption] I added new tests to check the change I am making, or this PR is [test-exempt].
- [Need to run] All existing and new tests are passing.

* isCanvasKit implement and test

* isCanvasKit implement and test

* ++

* forgot license

* make isCanvasKit a getter

* addressed comments

* forgot to change names of integration test files

* typo

* simplified tests

* comments