When an Expr object is changed and that Expr is referenced by an AggInfo, then

When an Expr object is changed and that Expr is referenced by an AggInfo, then
also update the AggInfo.  Also, persist all AggInfo objects until the Parse
object is destroyed.  This is a new fix for ticket [c8d3b9f0a750a529] that
avoids the follow-on problems identified by tickets
[0899cf62f597d7e7], [1f6f353b684fc708], [e5504e987e419fb0], and
[f7d890858f361402].

FossilOrigin-Name: 6e6b3729e0549de028f6c5bf494b2d69d621c81b61a1dc0a329d3950039342fb