Add a way to see all PRs where I have a pending (unsubmitted) review

[vnguyen-aquent]

🏷️ Discussion Type

Product Feedback

Body

Related to the long-running #10369 ("Make it clear that PENDING comments have
to be submitted") — but this is a more specific, additive ask rather than a
wording fix.

Today there's no way to see, across an org/repo, which PRs I've started a
review on but haven't submitted yet. The only way to discover this is to open
each PR individually and check the "Files changed" tab for the pending-review
banner — there's no search qualifier (is:pr review:pending or similar) and
no dashboard.

This is easy to lose track of, especially when you review several PRs in a
sitting and get interrupted before submitting one of them. The author has no
signal either — their PR just looks like nobody reviewed it, so requests to
"please review" go unanswered even though feedback already exists in draft
form.

Suggestion: surface this the same way review-requested:@me works today,
e.g.:

• A review:pending (or similar) qualifier for pull request search, scoped to
  the authenticated user's own draft reviews
• A count/badge on the Pull Requests dashard (github.com/pulls) for "Your
  pending reviews"
• Or, at minimum, surface it via the GraphQL/REST API so tools (bots, CLI,
  IDE extensions) can query it, since right now the only way to detect it
  programmatically is to fetch full review lists per-PR and filter for
  state: PENDING, which doesn't scale across an org.

This would directly help reviewers who use "Start a review" to batch
comments, which GitHub's own UI encourages, but currently offers no way to
track across more than one PR at a time.

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