fix(errors): "column x of relation y does not exist" is reported as "Table y does not exist" #1310

Problem

lib/core/database/database_error_mapper.dart:91 maps relation "([^"]+)" does not exist to TableNotFoundException. PostgreSQL's message for a missing column in an INSERT / UPDATE is column "x" of relation "t" does not exist, so the regexp captures t and the user reads Table "t" does not exist. Check the table name and schema... when the table exists and the column does not.

Scope

• Match the column form first and map it to a column message (Column "x" does not exist in "t", hint: check the column name or refresh the tree), or leave it as the original text.
• Anchor the relation pattern so it does not match inside the column form.
• Tests in the mapper's test file for both messages, plus MySQL's Unknown column 'x' in 'field list'.

Acceptance

• column "x" of relation "t" does not exist is not reported as a missing table.
• relation "t" does not exist still is.