Change `JsonNode.withObject(String)` to work similar to `withArray()` wrt argument

[cowtowncoder]

Describe your Issue

(see #3780 for lengthy background discussion)

New JsonNode.withObject(String) method added in 2.14 only allows for using String that is valid JsonPointer expression. This is different from existing withArray(String) method. While I earlier felt that the new behavior is more sensible, avoiding confusion, it seems many users feel otherwise.

As a consequence I think behavior should be changed for 2.16 to allow for "property-or-expression" -- this should be safe (enough) change and along with #4095 solve the issue.