Fix: Mssql introspection duplicate columns

[tmrclark]

Reproduction Repo

When using the MSSQL dialect, .introspect.getTables() returns duplicate columns in certain circumstances. A simple example is a column with the data type nvarcar. The output looks like

[
  {
    dataType: 'nvarchar',
    dataTypeSchema: 'sys',
    hasDefaultValue: false,
    isAutoIncrementing: false,
    isNullable: true,
    name: 'column_1'
  },
  {
    dataType: 'sysname',
    dataTypeSchema: 'sys',
    hasDefaultValue: false,
    isAutoIncrementing: false,
    isNullable: false,
    name: 'column_1'
  }
]

The Cause

This is a known issue caused by how MSSQL manages types internally. It surfaces in the .getTables method where the query joins sys.types to sys.columns on system_type_id when it should be using user_type_id

-- Returns 2 rows
SELECT c.name, ty.name, ty.system_type_id, ty.user_type_id
FROM sys.tables AS t 
INNER JOIN sys.columns AS c ON t.object_id = c.object_id
INNER JOIN sys.types AS ty ON ty.system_type_id = c.system_type_id
WHERE t.name = 'test_table'

VS

-- Returns 1 row
SELECT c.name, ty.name, ty.system_type_id, ty.user_type_id
FROM sys.tables AS t 
INNER JOIN sys.columns AS c ON t.object_id = c.object_id
INNER JOIN sys.types AS ty ON ty.user_type_id = c.user_type_id
WHERE t.name = 'test_table'