Fix bug GH-11941: soap with session persistence will silently fails when "seession" built as a shared object (#14362)

This adds an optional dependency on the session extension and adds the

Fix bug GH-11941: soap with session persistence will silently fails when "seession" built as a shared object (#14362)

This adds an optional dependency on the session extension and adds the
necessary APIs to make the functionality work with lazy binding.

This can be tested by configuring PHP with `--enable-session=shared` and
`--enable-soap=shared` and running the test suite, in particular the
buggy behaviour can be observed by the existing test `server009.phpt`.

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