Previously, StaticResourceJars would only find jars with
META-INF/resources content if it had been loaded by a URLClassLoader.
This is not the case on Java 9 and, as a result, static content in
META-INF/resources of any jars on the class path was not found.

This commit updates StaticResourceJars to fall back to using the
JVM's class path to find static resource jars when it was loaded by
a ClassLoader that is not a URLClassLoader.

Closes gh-10455