Close two paths that reach services past their intended gate

[chenBright]

What problem does this PR solve?

Issue Number: resolve

Problem Summary:

Paths that differ only in empty segments dispatched identically. FindMethodPropertyByURIImpl splits
the path with a StringSplitter that skips empty fields, so //flags, /flags// and /flags//port all resolved
to the same method as /flags. RFC 3986 treats //foo and /foo as distinct paths, so a front proxy whose
ACL matches the collapsed form does not match the padded one and passes it through — //flags?setvalue=
reaches a builtin service that /flags cannot. Normalizing the path server-side would not help, because the
proxy has already forwarded the padded literal; only rejecting it removes the differential.

The same audit found that HTTP/2 never validated :path. RFC 9113 8.3.1 requires it to be non-empty and,
apart from the asterisk-form used by OPTIONS, to begin with /.

What is changed and the side effects?

Changed:

• FindMethodPropertyByURI rejects any path containing //. The check lives in
  the funnel rather than in FindMethodPropertyByURIImpl, so it also covers the
  global restful map, which does its own NormalizeSlashes.
• H2StreamContext::ConsumeHeaders rejects a :path that is empty or does not
  begin with /, unless it is exactly *.

Side effects:

• Performance effects:

• Breaking backward compatibility:

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Check List:

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