Core: Pass down the types from the delete mapping request to the delete by query request.

The `.percolator` type is a hidden type and therefor the types from the delete mapping request should passed down to the delete by query request, otherwise the percolator type gets ignored and the percolator queries don't get deleted from disk (only unregistered).

Closes #7087
Internal: adjusted visibility of GetRequest members (from protected to private) and resolved warning
[DOCS] fixed DeleteIndexedScriptResponse javadocs
Core: Avoid null references that may be returned due to concurrent changes or inconsistent cluster state

Closes #7181
Mappings: Make sure that multi fields are serialized in alphabetic order to ensure that the source is always the same.

Closes #7215