Separate link openers for issues and pull requests #9082

Feature request

The extension registers a single external URI opener, <extension id>.issueOrPullRequest, labelled "Open GitHub Issue or Pull Request", for both issue and pull request links.

VS Code now lists the available openers when you paste a link into Quick Open (microsoft/vscode#342897, part of microsoft/vscode#342050), and shows them in the "How would you like to open" prompt. There, an issue link and a pull request link both read "Open GitHub Issue or Pull Request".

Expected

Register separate openers for issues and pull requests, for example "Open Issue" and "Open Pull Request", each claiming only its kind of link in canOpenExternalUri. The list then names what will open. It also lets users configure a default per kind in workbench.externalUriOpeners.

Keep the existing opener id working for users who configured it.