Similar reasoning as #18133 but for the aggs API. One important change is that
I moved the base PipelineAggregatorBuilder class to the o.e.s.aggregations
package instead of o.e.s.aggregations.pipeline so that the create method does
not need to be public.
Significant changes:
* AbstractQueryTestCase has moved to the test framework module, in order for query builder tests in modules and plugins
* Added support to AbstractQueryTestCase to register plugins
* Lift the restriction that only one percolator could be added per index. This validation existed in MapperService, but because the percolator moved to a module it could no longer exist there. Instead of bringing it back it was removed. This validation existed since the percolator cache only supported one percolator query per document, since the percolator cache has been removed this restriction could removed as well.
* While moving percolator tests to the new module, also removed a couple of tests for the deprecated percolate and mpercolate api. These APIs are now sugar APIs for bwc and rediect to the searvh and msearvh APIs. Some tests were still testing as if percolate and mpercolate API did the percolation, but this no longer the case and these tests could be removed.
Adrien Grand
Martijn van Groningen
Tanguy Leroux