Improvements of SQL introspection

[aljazerzen]

Currently, introspection over SQL adapter is a bit lacking. In some cases, we leak internal database structure that should not be visible to end users (i.e. schema edgedbpub) and in some cases we don't expose features because they don't exist in the internal database (foreign keys).

This issue is a tracking issue of all such problems:

• defaults - some tools look at pg_attribute to see if a column is AUTO generated or not. We don't use PostgreSQL defaults, but inject the defaults in our compilation process. We should set column pg_attribute.atthasdef for those columns and populate table pg_attrdef,
• primary keys - I don't know where, but id is not being picked up (by Django) as the primary key. Emulate introspection of primary keys over SQL adapter #7937
• foreign keys - ORMs depend on detecting foreign keys to translate them into links,
• format_type - is implemented incorrectly and should be redone fully Improve format_type over SQL adapter #7924,
• pg_tables and pg_views are not being populated, Fill-out pg_catalog introspection SQL adapter #6403
• FROM x JOIN y ON x.id = y.id WHERE id = 4 is not ambiguous (not really an introspection issue) Factoring of columns in USING clause over SQL adapter #7923

[aljazerzen]

We also need to decide on which schemas to expose. Currently, this is what is seen in an empty database:

pg_toast                -- PostgreSQL
pg_catalog              -- PostgreSQL
information_schema      -- PostgreSQL

edgedb_v6_2f209700f0    -- for module schema::
edgedb                  -- for module schema::, trampolined

edgedbstd_v6_2f209700f0 -- for module std::
edgedbstd               -- for module std::, trampolined

edgedbt 				-- for datetime types in std::

public                  -- for module default

I think we should:

• hide all trampolined schemas,
• rename edgedb into schema,
• rename edgedbstd into std,
• merge edgedbt into std.

Edit: where should we put types without edgedb module? Things like tuple<str, int64>? Currently, they appear in public, which might be confusing.