Update the performance improvements to push certificate loading
and storage into the `JarFileEntries` class. This allows us to
keep certificates without needing to cache all entry data. We
now also keep certificates and code signers in a dedicated class
which is set whenever the full jar stream as been read, even if
the contained values are `null`. The logic that assumes META-INF
entries are not signed has been removed in favor of delegating to
the streamed entry results.

See gh-19041