feat: allow overriding comment icons

[BeksOmega]

The basics

• I validated my changes

The details

Resolves

Fixes #7910
Fixes #7911

Proposed Changes

Allows comment icons to be overriden, and constructed from Block.prototype.setCommentText.

Reason for Changes

This will allow external partners to create their own comment icons (e.g. that use the new CommentView, while still using the built-in functionality like setCommentText, context menu options, etc.

Test Coverage

Added tests that setCommentText properly constructs classes from the registry.

Documentation

Yesh, we'll need to document the fact that you can do this somewhere.

Additional Information

N/A

[BeksOmega]

Forgot to check for setBubbleSize and getBubbleSize

[maribethb]

I guess I thought this was intentional because if we're checking from Block then it could be headless so they don't need to care about bubble size necessarily. But I guess if they only care about headless they prooobably don't have a need to override the class to begin with?

[BeksOmega]

Headless ones also need to have these methods so that the size properly gets round-tripped through serialization.

I also didn't think they were necessary, and I actually left those methods out originally. I only added them to the interface when I ran into the compiler errors :P Which is why I forgot to add them to the type guard.