Move IndexFieldDataServiceTests into corresponding package
Move MockDirectories into o.e.test.store
Move o.e.junit to o.e.test.junit
Move stresstests out of o.e.test
Fixed fetch subphase to not recreate the HitContext for each hit, so that the object cache stays the same

Fixed also bug in the fast vector highlighter which was raised by enabling the object cache, due to null FieldQuery (NPE) in case the objects are taken from the cache

Added tests to check if there are issues when highlighting multiple fields at the same time

Closes #4106
Trimmed down HighlighterSearchTests

Used common assertHighlight and concise mapping whenever possible
More indexRandom too
Fix missing affectation in SimpleChildQuerySearchTests.testParentChildQueriesCanHandleNoRelevantTypesInIndex()
[DOCS] Changed all store:yes/no to store:true/false
which is how this setting is stored internally
[DOCS] Fixed the fielddata regex example on core mapping
Used the actual index_name when making highlighting using the postings highlighter

Previously the field name specified in the search request was used, which isn't correct in case a custom index_name has been used for a field or the "path":"just_name" has been used in the mapping.

 Closes #4116