Move SLF4J artifacts to boot classloader

[kwin]

This makes it possible to use the SLF4J System.LoggerFinder This is looked up with ClassLoader.getSystemClassLoader(). This also requires the SLF4J API to be provided in that classloader.

This closes #11684

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[cstamas]

This is not so simple.

See here:

maven/apache-maven/src/bin/mvn

Line 211 in 5bcfc50

-classpath "${CLASSWORLDS_JAR}" \

and then here:
https://github.com/apache/maven/blob/5bcfc50834638b7798cc699c7d460e564b0eedb8/apache-maven/src/bin/m2.conf

We use classworlds launcher (that is refd in mvn script, and loads m2.conf):
https://codehaus-plexus.github.io/plexus-classworlds/launcher.html