[web] fix SkFinalizationRegistry for dart2js (attempt 4) (#40938)

(this is attempt 4; details below)

Remove obsolete object caches and introduce a simpler way to manage
native objects:

* Remove the unused `SynchronousSkiaObjectCache`.
* Introduce new library `native_memory.dart` that's smaller and simpler
than `skia_object_cache.dart`.
* Introduce two types of native object references:
  * `UniqueRef` a reference with a unique Dart object owner.
* `CountedRef` a ref-counted reference with multiple Dart object owners.
* All native references use GC (via `FinalizationRegistry`) as a
back-up.
* The new library removes everything related to object resurrection that
was needed only in browsers that didn't support `FinalizationRegistry`.
All browsers support it now.
* Remove the ad hoc `SkParagraph` cache that predates the introduction
of `Paragraph.dispose`.
* Rewrite `CkParagraph` in terms of `UniqueRef`.
* Rewrite `CkImage` in terms of `CountedRef`; delete `SkiaObjectBox`.

This PR does not migrate all objects from the old
`skia_object_cache.dart` to `native_memory.dart`. That would be too big
of a change. The migration can be done in multiple smaller PRs.

This also removes a few unnecessary relayouts observed in
https://github.com/flutter/flutter/issues/120921, but not all of them
(more details in
https://github.com/flutter/flutter/issues/120921#issuecomment-1481958762)

## About attempt 4

More info about the revert of attempt 3 in
https://github.com/flutter/engine/pull/40937.

In this attempt I check that the browser supports `FinalizationRegistry`
before registering the object. This will allow the code to run in older
browsers, but there will be no protection from memory leaks when the app
fails to dispose of the respective objects.

## Benchmarks

Now that this landed in flutter/flutter I have some benchmark numbers
from the devicelab. The `text_out_of_picture_bounds` benchmark dropped
by 3-4x (lower is better):

<img width="358" alt="Screenshot 2023-04-04 at 6 13 06 PM"
src="https://user-images.githubusercontent.com/211513/229956170-a5399ed3-c779-4af0-babb-ea40440f96ff.png">

The repro provided in https://github.com/flutter/flutter/issues/123204
dropped from 110ms/frame to 10ms/frame.