remove analyzers subdirectory in 5.3 [LUCENE-6574]

This stupid setup makes our build so complex, I remember having to do it with a gun to my head because people just love overengineering shit.

there is no reason for this: it can be flattened and analyzers-common/ and so on can just be besides everything else.

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Migrated from [LUCENE-6574](https://issues.apache.org/jira/browse/LUCENE-6574) by Robert Muir (@rmuir)

Start by mapping the analyzers subdirectory and the sibling modules named in the issue, including analyzers-common, then inspect the build configuration that creates this layout. Confirm whether flattening the directories is still relevant to the 5.3 setup and identify the build checks needed to show that all analyzers modules remain available after the change.

Written by the indexing model from the issue text.