[1.7.x] Fixed #3214 -- Stopped parsing SQL with regex.

Avoided introducing a new regex-based SQL splitter in the migrations
framework, before we're bound by backwards compatibility.

Adapted this change to the legacy "initial SQL data" feature, even
though it's already deprecated, in order to facilitate the transition
to migrations.

sqlparse becomes mandatory for RunSQL on some databases (all but
PostgreSQL). There's no API to provide a single statement and tell
Django not to attempt splitting. Since we have a more robust splitting
implementation, that seems like a good tradeoff. It's easier to add a
new keyword argument later if necessary than to remove one.

Many people contributed to both tickets, thank you all, and especially
Claude for the review.

Refs #22401.

Backport of 8b5b199 from master

tests/migrations/test_operations.py

@@ -1,5 +1,10 @@
 import unittest
 
+try:
+    import sqlparse
+except ImportError:
+    sqlparse = None
+
 from django.db import connection, migrations, models, router
 from django.db.migrations.migration import Migration
 from django.db.migrations.state import ProjectState
@@ -640,6 +645,7 @@ class OperationTests(MigrationTestBase):
             operation.database_backwards("test_alinto", editor, new_state, project_state)
         self.assertIndexNotExists("test_alinto_pony", ["pink", "weight"])
 
+    @unittest.skipIf(sqlparse is None and connection.features.requires_sqlparse_for_splitting, "Missing sqlparse")
     def test_run_sql(self):
         """
         Tests the RunSQL operation.
@@ -647,7 +653,10 @@ class OperationTests(MigrationTestBase):
         project_state = self.set_up_test_model("test_runsql")
         # Create the operation
         operation = migrations.RunSQL(
-            "CREATE TABLE i_love_ponies (id int, special_thing int)",
+            # Use a multi-line string with a commment to test splitting on SQLite and MySQL respectively
+            "CREATE TABLE i_love_ponies (id int, special_thing int);\n"
+            "INSERT INTO i_love_ponies (id, special_thing) VALUES (1, 42); -- this is magic!\n"
+            "INSERT INTO i_love_ponies (id, special_thing) VALUES (2, 51);\n",
             "DROP TABLE i_love_ponies",
             state_operations=[migrations.CreateModel("SomethingElse", [("id", models.AutoField(primary_key=True))])],
         )
@@ -661,6 +670,10 @@ class OperationTests(MigrationTestBase):
         with connection.schema_editor() as editor:
             operation.database_forwards("test_runsql", editor, project_state, new_state)
         self.assertTableExists("i_love_ponies")
+        # Make sure all the SQL was processed
+        with connection.cursor() as cursor:
+            cursor.execute("SELECT COUNT(*) FROM i_love_ponies")
+            self.assertEqual(cursor.fetchall()[0][0], 2)
         # And test reversal
         self.assertTrue(operation.reversible)
         with connection.schema_editor() as editor: