Allow relative and anchor links in link edit menu, and allow users to override link-formatting behavior

[sjdemartini]

Resolves: #182 and #275

Changes:

• The default behavior of the LinkBubbleMenu editing is to do the following to the user-entered URL when they finish typing:
  • trim leading/trailing whitespace (unchanged)
  • ensure the value has a protocol (http://) if it doesn't already and isn't a relative (starting with "/") or anchor (starting with "#") URL (change in behavior)
    • Change: We now accept relative URLs starting with "/" and anchor links starting with "#" (resolves Allow to add internal links using EditLinkMenuContent #275)
    • Change: We now also accept sms: as a valid protocol, like we did for mailto: and tel: before
  • URL-encode the result (unchanged)
• The input field is now of type text instead of url to support relative URLs. So it will be less strict in enforcing URL formatting.
• LinkBubbleMenu now has a formatHref prop which can be used to override the above link-formatting behavior and provide custom functionality (resolves How do I skip the formatHref behavior? #182)