refactor!: Rename EditComment to UpdateComment on PullRequestsService, split review comment request bodies, and pass by value

[JamBalaya56562]

Continues the request-body-by-value work in #3644, this time for the review comment endpoints on PullRequestsService — the pulls counterpart of #4444.

Commit 1 (refactor!:) — CreateComment and EditComment reused the 27-field PullRequestComment response type as their request bodies, and EditComment's doc comment had to warn:

A non-nil comment.Body must be provided. Other comment fields should be left nil.

Per the docs, the two schemas differ, so the body is split (same approach as #4382/#4401/#4438):

Field	Create (POST)	Update (PATCH)
body	required	required (only parameter)
commit_id, path	required	—
line, start_line, start_side	conditionally required ("required unless …") → stay pointers	—
side, in_reply_to, subject_type	optional	—
position	optional, deprecated → kept with a // Deprecated: note	—

• CreatePullRequestCommentRequest — Body/CommitID/Path are non-pointer since they're unconditionally required; the conditionally-required line fields stay pointers (same treatment as title in refactor!: Rename NewPullRequest to CreatePullRequest and pass it by value #4395). Note the request tag is in_reply_to, not the response's in_reply_to_id.
• UpdatePullRequestCommentRequest — just Body string.

EditComment is renamed to UpdateComment to match the docs operation name (same convention as #4444). CreateCommentInReplyTo already builds its own minimal body internally and is unchanged. PullRequestComment is removed from the body-allowed-pointer-types allowlist.

Commit 2 (feat:) — while cross-checking the response schema (prompted by the review feedback on #4444 and #4477, where missing response fields were caught by reviewers), I found three properties missing from PullRequestComment and added them up front: BodyHTML, BodyText, and Links (_links, modeled with a new PullRequestCommentLinks type reusing the existing PRLink).

Verified with go build ./..., go vet -tags integration ./test/integration/, gofmt, the full ./github/ test suite (CreateComment/UpdateComment and the generated accessors at 100%), and custom-gcl (no paramcheck findings after removing the allowlist entry).

Updates #3644

BREAKING CHANGE: PullRequestsService.CreateComment now takes a new CreatePullRequestCommentRequest (with non-pointer Body, CommitID and Path) by value, and PullRequestsService.EditComment is renamed to UpdateComment and takes a new UpdatePullRequestCommentRequest by value, instead of *PullRequestComment.

cc @jvm986 — flagging for #3644 coordination; this is the pulls comments type, so no overlap with your recent work.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.53%. Comparing base (34cec4f) to head (b3a119b).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #4493   +/-   ##
=======================================
  Coverage   98.53%   98.53%           
=======================================
  Files         195      195           
  Lines       17691    17691           
=======================================
  Hits        17431    17431           
  Misses        260      260           

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[gmlewis]

Thank you, @JamBalaya56562!
LGTM.
Awaiting second LGTM+Approval from any other contributor to this repo before merging.

cc: @stevehipwell - @alexandear - @Not-Dhananjay-Mishra