[V1] Add SQL PATH support to function resolution

[RCHowell]

Relevant Issue/Bug

#1496

Requested Solution/Feature

• Session PATH is searched to resolve functions
• A catalog provides methods for looking up functions

Describe Alternatives

None, this is SQL standard.

Additional Context

SQL-99 Part 2, 4.25 SQL-paths

The value specified by CURRENT_PATH is the value of the SQL-path of the current SQL-session. This SQL-path is used to search for the subject routine of a whose does not contain a when the is contained in s that are prepared in the current SQL-session by either an or a , or contained in s that are invoked directly. The definition of SQL-schemas specifies an SQL-path that is used to search for the subject routine of a whose s do not contain a when the is contained in the .

Feature S071, ‘‘SQL-paths in function and type name resolution’’

DoD (Definition of Done)

A catalog provides functions (just like tables) and the resolution/lookup strategy follows the SQL specification rules for searching the PATH.