Expose read-isolation parameters in 'Database.read'/'Database.execute_sql'

[tseaver]

And therefore in Snapshot.read / Snapshot.execute_sql.

And therefore in Session.read / Session.execute_sql

From #3615 (comment)

[vkedia]

I dont think Snapshot.read and Snapshot.execute_sql should take in isolation parameters since all reads/queries within a multi use snapshot should use the same isolation. So it will be confusing if users can specify those as a parameters for read/query.
Database.read and Database.execute_sql shouls take in these parameters and pass those to the constructor of snapshot.

[tseaver]

Oops, I mean to say Session.read and Session.execute_sql (because those are the ones called by Database.read / Database.execute_sql.

[vkedia]

Any updates on this?

[tseaver]

#3787 is removing those methods (because #3769).