SOLR-16203: Initialize schema plugins loaded by SPI name

[janhoy]

https://issues.apache.org/jira/browse/SOLR-16203

[janhoy]

First attempt in efadf94:

Naïve solution, explicitly calling inform() in FieldTypePluginLoader. The two tests from JIRA are added to this PR to demonstrate.

There may be a more elegant place to do the init. We risk double inform if not using SPI since we don't check that here. Perhaps there is some method somewhere that could be called on the entire chain instead of in each init(), such as the one in ManagedIndexSchema#informResourceLoaderAwareObjectsInChain(). I did not dive deep here. Open to suggestions from folks who know the code better.

[janhoy]

Second attempt:

The first attempt did not work for packages, since FieldTypePluginLoader#init was too early in the cycle to initialize analyzers from packages.

Managed schema handled the missing inform call after SPI already, so moved the method informResourceLoaderAwareObjectsForFieldType from ManagedIndexSchema to IndexSchema and use it at the end of IndexSchema#readSchema. All tests pass.

[janhoy]

Thanks for nice proposals @uschindler , the method is now private and code cleaner