Improve exception message when EF.Function is evaluated on the client.

[maumar]

EF Functions throw FunctionOnClient exception when they are actually invoked (rather than translated to SQL).
Currently the message is as follows:

The '{methodName}' method is not supported because the query has switched to client-evaluation. This usually happens when the arguments to the method cannot be translated to server. Rewrite the query to avoid client evaluation of arguments so that method can be translated to server.

This could also happen in the funcletizer, when the function is evaluatable (i.e. no arguments are correlated to the model but rather they are all constants). We should add that information to the exception