SOLR-6145: Fix Schema API optimistic concurrency by moving it out of ManagedIndexSchema.add(Copy)Fields() into the consumers of those methods: CopyFieldCollectionResource, FieldCollectionResource, FieldResource, and AddSchemaFieldsUpdateProcessorFactory. (merged trunk r1601770 and r1601775)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1601776 13f79535-47bb-0310-9956-ffa450edef68