There is a bug in CanvasKit where a backdrop filter with a platform view
as a child will cause the backdrop filter to apply multiple times. This
change fixes it by only applying the backdrop filter once.

The bug case is more likely to happen since
https://github.com/flutter/engine/pull/47317 landed because when we
encounter an invisible platform view, we always create a new SkPicture
instead of continuing to use the same SkPicture.

BEFORE:

![canvaskit_backdropfilter_with_platformview_BAD](https://github.com/flutter/engine/assets/1961493/c1fa766f-ebf7-4468-9ea7-8ab0d51314c7)

AFTER:

![canvaskit_backdropfilter_with_platformview](https://github.com/flutter/engine/assets/1961493/57d27d62-ee49-43a2-af3f-e532aaba0ffb)


## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide] and the [C++,
Objective-C, Java style guides].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I added new tests to check the change I am making or feature I am
adding, or the PR is [test-exempt]. See [testing the engine] for
instructions on writing and running engine tests.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I signed the [CLA].
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
on [Discord].

<!-- Links -->
[Contributor Guide]:
https://github.com/flutter/flutter/wiki/Tree-hygiene#overview
[Tree Hygiene]: https://github.com/flutter/flutter/wiki/Tree-hygiene
[test-exempt]:
https://github.com/flutter/flutter/wiki/Tree-hygiene#tests
[Flutter Style Guide]:
https://github.com/flutter/flutter/wiki/Style-guide-for-Flutter-repo
[C++, Objective-C, Java style guides]:
https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style
[testing the engine]:
https://github.com/flutter/flutter/wiki/Testing-the-engine
[CLA]: https://cla.developers.google.com/
[flutter/tests]: https://github.com/flutter/tests
[breaking change policy]:
https://github.com/flutter/flutter/wiki/Tree-hygiene#handling-breaking-changes
[Discord]: https://github.com/flutter/flutter/wiki/Chat