Fixed #32632, Fixed #32657 -- Removed flawed support for Subquery deconstruction.

Subquery deconstruction support required implementing complex and
expensive equality rules for sql.Query objects for little benefit as
the latter cannot themselves be made deconstructible to their reference
to model classes.

Making Expression @deconstructible and not BaseExpression allows
interested parties to conform to the "expression" API even if they are
not deconstructible as it's only a requirement for expressions allowed
in Model fields and meta options (e.g. constraints, indexes).

Thanks Phillip Cutter for the report.

This also fixes a performance regression in bbf141bcdc.

tests/queries/test_q.py

@@ -1,4 +1,5 @@
-from django.db.models import Exists, F, OuterRef, Q
+from django.db.models import BooleanField, Exists, F, OuterRef, Q
+from django.db.models.expressions import RawSQL
 from django.test import SimpleTestCase
 
 from .models import Tag
@@ -50,6 +51,16 @@ class QTests(SimpleTestCase):
         with self.assertRaisesMessage(TypeError, str(obj)):
             q & obj
 
+    def test_combine_negated_boolean_expression(self):
+        tagged = Tag.objects.filter(category=OuterRef('pk'))
+        tests = [
+            Q() & ~Exists(tagged),
+            Q() | ~Exists(tagged),
+        ]
+        for q in tests:
+            with self.subTest(q=q):
+                self.assertIs(q.negated, True)
+
     def test_deconstruct(self):
         q = Q(price__gt=F('discounted_price'))
         path, args, kwargs = q.deconstruct()
@@ -101,10 +112,10 @@ class QTests(SimpleTestCase):
         self.assertEqual(kwargs, {})
 
     def test_deconstruct_boolean_expression(self):
-        tagged = Tag.objects.filter(category=OuterRef('pk'))
-        q = Q(Exists(tagged))
+        expr = RawSQL('1 = 1', BooleanField())
+        q = Q(expr)
         _, args, kwargs = q.deconstruct()
-        self.assertEqual(args, (Exists(tagged),))
+        self.assertEqual(args, (expr,))
         self.assertEqual(kwargs, {})
 
     def test_reconstruct(self):