Cleanup http methods typings

[kanongil]

This fixes several issues with the current http method verb handling:

1. Explicit list all possible verbs for request.route() definitions, including '*'.
2. Disallow using string for request.route() method, since it made it prone to misspellings.
3. Only allow lowercased verbs including 'head' for request.method (fixes HTTP_METHODS_PARTIAL_LOWERCASE is missing head #4492).
4. Only allow lowercased verbs and '*' values for request.route.method.
5. Allow 'HEAD' and lowercased verbs for request.setMethod().

As with any changes to the typings, this can break the type checks in projects that use hapi. I expect this will mostly just work, but there can be esoteric cases where some work will be required to fix it after updating.

[Marsup]

That's perfect, I'll merge asap. Just rebasing because I think you fixed the failing tests in another PR.