refactor: rename drop_db / drop_database to drop_all_tables, expose database from connection (#2098)

If we start supporting external catalogs then "drop database" may be
misleading (and not possible). We should be more clear that this is a
utility method to drop all tables. This is also a nice chance for some
consistency cleanup as it was `drop_db` in rust, `drop_database` in
python, and non-existent in typescript.

This PR also adds a public accessor to get the database trait from a
connection.

BREAKING CHANGE: the `drop_database` / `drop_db` methods are now
deprecated.

python/python/tests/test_db.py

@@ -499,6 +499,10 @@ def test_delete_table(tmp_db: lancedb.DBConnection):
     # if ignore_missing=True
     tmp_db.drop_table("does_not_exist", ignore_missing=True)
 
+    tmp_db.drop_all_tables()
+
+    assert tmp_db.table_names() == []
+
 
 @pytest.mark.asyncio
 async def test_delete_table_async(tmp_db: lancedb.DBConnection):