test(mssql): add MSSQL end-to-end test for column_as

Add MSSQL variant of the column_as test to verify basic SELECT
with column aliases works correctly with the MSSQL engine.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: claude

internal/endtoend/testdata/column_as/mssql/go/db.go

@@ -0,0 +1,5 @@
+-- name: WithAs :one
+SELECT 1 AS x, 2 AS y;
+
+-- name: WithoutAs :one
+SELECT 1 x, 2 y;

internal/endtoend/testdata/column_as/mssql/go/models.go

@@ -0,0 +1,11 @@
+version: "2"
+sql:
+- schema: schema.sql
+  queries: query.sql
+  engine: mssql
+  database:
+    uri: ${MSSQL_SERVER_URI}
+  gen:
+    go:
+      package: querytest
+      out: go