[ClassLoader] Add a __call() method to XcacheClassLoader
bug #11768 [ClassLoader] Add a __call() method to XcacheClassLoader (tstoeckler)

This PR was squashed before being merged into the 2.3 branch (closes #11768).

Discussion
----------

[ClassLoader] Add a __call() method to XcacheClassLoader

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11733
| License       | MIT
| Doc PR        |

Commits
-------

dd0d6af [ClassLoader] Add a __call() method to XcacheClassLoader