Directly forward the uri when it's a path instead of trying to parse it.

Also clean up isOriginForm/isAsteriskForm as their logic seems to be incorrect (for example, URI#getSchemeSpecificPart() never returns null so they both return false trivially). They should probably be edited themselves in a later commit (and possibly used again here when correct). Since this was always returning true, it's unclear if authority logic is still correct after this change.

Add tests to ensure request conversion behaves as expected.

Fix test failures. This requires refactoring the authority pathway to
reflect what it was in practice before (though not what the logic
implied).

Specifically, the logic before never set the HTTP2 Authority if the path
was in origin or asterisk form (although due to those methods always
returning false this never affected output).