Configuration: Tab characters in YAML should throw an exception.

Throw an exception if there is a 'tab' character in the elasticsearch.yml file

Close #8259
Core: In the bitset cache only eagerly load bitsets for parent nested object fields.
Don't eagerly cache parent type filters in bitset cache or nested object fields that are leafs.

Also let parent/child queries not rely on FixedBitSetFilter, but rather on regular Filter

Closes #8440
Aggregations: Changed child filters to not require a random access based bitset in `nested` agg.

Also the nested agg now requires docs to be consumed / scored in order.
Applied feedback.