Add can-change-port extension

[jessetrinity]

This is a followup to the ssh version check change that was done when open sourcing the library. This allows us to not rely on the version name for the port switching behavior.

• Add a new can-change-port extension to indicate whether the ssh implementation supports changing ports.
• The isVsSsh check (which does this same thing) should be retained for older versions of the library which don't support the extension.
• Removes the isVsSsh check where it is no longer needed (for versions 2.x).
• Bump the minor version.

[jasongin]

Were you planning to remove the Name == "Microsoft.DevTunnels.Ssh" check from IsVsSsh()?

[jessetrinity]

Were you planning to remove the Name == "Microsoft.DevTunnels.Ssh" check from IsVsSsh()?

Won't that cause issues with the (few) already published versions using that name?

[jasongin]

Won't that cause issues with the (few) already published versions using that name?

Yes.