Deprecate FunctionNode without TypedExpression

In next major version we should make DQL TypedExpression a part of FunctionNode, which requires to deprecate it first in 2.x

This was introduced in #7941

Also related to #8025 - where identity now converts types. This is actually starts converting now, which we should consider a BC break.

What about introducing a query hint that starts converting function nodes, and when the query hint is not set, then we emit a deprecation?

Start by reading FunctionNode and TypedExpression, then review the context in issues #7941 and #8025. The work is not ready to pick up until the deprecation plan, query-hint behavior, and backward-compatibility expectations are decided; done would be an agreed and documented 2.x transition path.

Written by the indexing model from the issue text.