Add p4 to right-click menu

[shaonianruntu]

Can you support clicking some option like "p4 annoate" in the vscode right-click menu to display a preview of the annoate information for the current line.

Add some options of p4 in the right-click menu:

[mjcrouch]

Hi, I would definitely like to have line level annotation on an open file, but technically I think it's pretty difficult for perforce to work out local changes. This feature would be heavily tied to #69 if I ever manage to work out how to do that.