[ObjC] Command for jumping directly to implementation of a selector by name

[bdash]

What is the feature you'd like to have? Add a command that allows the user to enter an Objective-C selector, matches it against known selectors in the binary, and jumps to the implementation of that selector. If more than one class implements the selector, the user should be able to select which implementation to jump to.

Workaround:

Search for sel_<selectorName> in the symbols list, navigate to it, then navigate to the implementation via the cross references pane.

Additional Information: Requested by a user on public Slack.