fix(elasticsearch): fix filtering on nested fields

[colinodell]

Q	A
Branch?	3.1
Tickets	#7997 and #5642
License	MIT
Doc PR	n/a

This PR implements the following changes to support filtering on paths like foo.bar.baz:

1. If foo is an object, isNestedField() now returns true instead of false
2. If foo is an object, getNestedFieldPath() now returns "foo.bar" instead of null
3. If foo is a collection, getNestedFieldPath() now returns "foo.bar" instead of just "foo" (matching the behavior if foo is an object)

As a result, filtering on deeply-nested paths (with 3 or more levels) now produces the following query:

 {
"nested": {
- "path": "foo",+ "path": "foo.bar",
"query": {
"term": {"foo.bar.baz": "qux"}
}
}
}
}

[soyuka]

nice please target main as it's a new feature right?

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.