Support functions with schema prefix

[kliushnichenko]

Example

CREATE TABLE foo
(
    entity_id        UUID PRIMARY KEY DEFAULT public.getId(),
    name             VARCHAR(64),
    CONSTRAINT my_constraint  CHECK(v2.my_function(name) IS TRUE)
);

Currently, if the reference to the function contains schema (public. and v2. in the example above) parser returns an empty result.
Would be nice to support this case as well.