Thanks to @bagtoad, this commit refactors the argument to `NewCopilotReplacer(bool)` from being where this is used to what it effect is has.
Because there is already precedence for display name being `<login> (<name>)`, I worried there would be confusion for `Copilot (AI)` being display name for assignees and reviewers but `Copilot` when going to GitHub.com UI. Instead, I renamed the argument based on whether the login is returned / replaced.
This commit is primarily focused on fixing the existing `gh issue create` tests with the changes to the underlying queries retrieving the data for resolving metadata.
Additionally, a new test case for `gh issue create --web --assignee @copilot` was added to mirror existing tests. While exercising this capability, I found out the web UI apparently wants `copilot` instead of the `copilot-swe-agent` login, so changes to address that were a part of this commit.
