fix(typecheck): don't substitute output columns or qualified columns as parameters

[psteinroe]

The database type check no longer replaces RETURNS TABLE/OUT columns, or qualified column references like r.received_at, with parameter literals in LANGUAGE sql bodies. The issue's function no longer reports non-integer constant in ORDER BY.

Only input parameters are in scope

get_sql_fn_signature collected every parameter, OUT and TABLE included. Postgres only exposes input parameters (IN, INOUT, VARIADIC) to the body, by name and as $n (get_func_input_arg_names, called from prepare_sql_fn_parse_info). Output columns are now skipped. That also fixes $n numbering when an OUT parameter comes before an input, and the static resolver: SELECT x with OUT x int is now reported as an unknown column, as Postgres does. Before, x counted as a parameter and nothing was reported.

Qualified names follow Postgres' rules

find_matching_identifier used to match a parameter name at any position in a dotted path, so r.received_at matched a parameter named received_at. It now accepts only the forms in sql_fn_post_column_ref: param, fn_name.param, param.field and fn_name.param.field, with fn_name.param taking precedence. Any other qualifier is a column reference and is left alone. Qualified references are not excluded outright, because fn_name.param and composite fields (#705) are valid parameter references.

Not in this PR

Postgres never lets a parameter override a table column (if (var != NULL) return NULL). The EXPLAIN check doesn't know which columns are in scope, so an unqualified reference that names both an input parameter and a column, e.g. f(id bigint) … ORDER BY id, is still replaced by a literal. The same applies to param.field when param is also a FROM alias. Fixing this needs scope information from the resolver, so it is left for a follow-up.

Fixes #835