Add more helpers that were needed for internal migrations (#552)

* Add more helpers that were needed for internal migrations

- 3.12 is required to support isA check on Object?
- More enum values are added, including NodeFilterEnum
(named as such because NodeFilter is already defined as
a typedef) and ScrollAlignment.
- More event streams are added.
- @Equivalence is a new annotation that instructs users
and tools of dart:html-equivalent members.
- A large number of extension members are added with
@Equivalence annotations to bridge common APIs.
- *Glue extensions are removed/renamed, and extensions
are largely unified to be 1-1 per type with the exception
of cross-origin helpers and streams.
- Various wrapper interfaces are added like CssRect,
CssClassSet, AttributeMap, StorageMap, and StringConsole
to bridge the wrapper classes that dart:html provided.
These are copied over as-is and have automated lint fixes
applied on them and any potential JS interop
incompatibilities addressed.
- openCrossOrigin now supports more parameters to reflect
dart:html's Window.open.
- Renames are re-added for migration convenience until
tooling makes the renaming more automated. I aim to remove
these before releasing v2.

* Analyzer issues

* Add deprecated_member_use_from_same_package lint to test_fixes option

* Gemini review comments

* Fix up minor divergences and format

* Review comments

* sealed -> final as sealed can't be instantiated