Djblets's JavaScript extension code is typed, but our Review Board

aliases were all classic code aliasing to the RB namespace directly.

This prevented any extensions from benefiting from any typing

information for classes, attribute interfaces, or anything else.
We now export those out from appropriate modules in order to retain all

the typing.
However, since the rest of the extension hooks depended on those being

set on RB, and were a bit of a pain to use from TypeScript code, this

change also converts those to TypeScript.
The hooks are very basic, so this is pretty straight-forward. We have

our usual attribute interfaces and our classes. The addition to the

existing code is that there's now dedicated *HookView classes for the

hooks that inject views into other views and pass in particular

attributes. The new views type and assign options so that usage is more

clear and types carry forward.
This is all going into a reviewboard/extensions module, rather than

being rolled up into reviewboard/common, in order to more clearly

separate common interfaces from extension-related code. It is, however,

being merged into the same Pipeline bundle, since pages including the

common bundle expect RB.Extension, the hooks, etc. to exist (which

is also needed for extensions not using ESM).

Unit tests passed.
Tested a few extensions, each making use of these classes. They were

still working as expected.
Ported one (rbcommenttype) to TypeScript and tested again. This tested

CommentDialogHook and ReviewDialogCommentHook. They still work.