Improve AssertSql for non-query tests

We're starting to have a lot of tests which don't derive from QueryTestBase, but which assert on SQL: everything deriving from NonSharedModelTestBase, JsonUpdateTestBase, etc. These use a simplified AssertSql which doesn't print a new baseline on failure, nor does it support automatic rewriting of baselines via EF_TEST_REWRITE_BASELINES=1. This makes it difficult to maintain these tests when many baselines are changed etc.

It would be great if we had the same level of AssertSql functionality for these tests.

/cc @maumar