Add support for period character in table names (#7453)

* Move schema name handling in table names from frontend to backend

* Rename all_schema_names to get_all_schema_names

* Fix js errors

* Fix additional js linting errors

* Refactor datasource getters and fix linting errors

* Update js unit tests

* Add python unit test for get_table_names method

* Add python unit test for get_table_names method

* Fix js linting error

superset/utils/core.py

@@ -32,7 +32,7 @@ import signal
 import smtplib
 import sys
 from time import struct_time
-from typing import List, Optional, Tuple
+from typing import List, NamedTuple, Optional, Tuple
 from urllib.parse import unquote_plus
 import uuid
 import zlib
@@ -1100,3 +1100,8 @@ def MediumText() -> Variant:
 
 def shortid() -> str:
     return '{}'.format(uuid.uuid4())[-12:]
+
+
+class DatasourceName(NamedTuple):
+    table: str
+    schema: str