This required upgrading some test dependencies, because the tests need some impls of the APIs which only exist in newer releases.
This also removes the struts2 extension from the maven & bazel build (although it keeps the now-unused source), because struts2 has no release that supports jakarta. For users that want to continue using the struts2 extension, please continue to use the Guice 6.0 release (instead of the 7.0+ line, which will only support the jakarta dependencies).
Fixes#1383.
(I'll cut the 6.0 candidates/releases from before this commit, and if we need to make further 6.0 changes, I'll manually merge those into the 6.0 branch.)
PiperOrigin-RevId: 529504991
