feat(pr): add changeType field to files JSON output

Add the changeType field from the PullRequestChangedFile GraphQL type
to the PullRequestFile struct. This exposes the file status (added,
modified, deleted, renamed, copied, changed) in gh pr list --json files
and gh pr view --json files output.

Closes #11385

api/query_builder.go

@@ -148,7 +148,8 @@ var prFiles = shortenQuery(`
 		nodes {
 			additions,
 			deletions,
-			path
+			path,
+			changeType
 		}
 	}
 `)