The ReviewRequestApprovalHook docs were pretty old and did little to

communicate the expectations of the hook. The very first sentence said

these were new in Review Board 2.0.
This change reworks the docs to clearly describe what approval state is

for and where it's used, the execution and chaining model of these

hooks, the signature of is_approved() methods, examples, and best

practices.
Typing and docs for the affected codepaths have been updated as well to

reflect what's shown in the guide and to link back to it.

Built the docs and checked the references/links on all affected code.
Ran content through ChatGPT for analysis and suggestions.