Add all structured objects passed to pushJsonbValue piecewise.

Commit 9b74f32c did this for objects of
type jbvBinary, but in trying further to simplify some of the new jsonb
code I discovered that objects of type jbvObject or jbvArray passed as
WJB_ELEM or WJB_VALUE also caused problems. These too are now added
component by component.

Backpatch to 9.4.