Put BlockingTrioPortal back where it's supposed to be.

When it was deprecated in python-triogh-1122, it accidentally got moved into
trio.hazmat.

Fixes: python-triogh-1167

newsfragments/1167.bugfix.rst

@@ -0,0 +1,3 @@
+In v0.12.0, we accidentally moved ``BlockingTrioPortal`` from ``trio``
+to ``trio.hazmat``. It's now been restored to its proper position.
+(It's still deprecated though, and will issue a warning if you use it.)

trio/__init__.py

@@ -115,6 +115,13 @@
             "0.12.0",
             issue=810,
         ),
+    "BlockingTrioPortal":
+        _deprecate.DeprecatedAttribute(
+            _BlockingTrioPortal,
+            "0.12.0",
+            issue=810,
+            instead=from_thread,
+        ),
 }
 
 _deprecate.enable_attribute_deprecations(hazmat.__name__)
@@ -143,13 +150,6 @@
             "0.12.0",
             issue=878,
         ),
-    "BlockingTrioPortal":
-        _deprecate.DeprecatedAttribute(
-            _BlockingTrioPortal,
-            "0.12.0",
-            issue=810,
-            instead=from_thread,
-        ),
 }
 
 # Having the public path in .__module__ attributes is important for:

trio/tests/test_threads.py

@@ -560,3 +560,9 @@ def worker_thread(token):
 
     t = await to_thread_run_sync(worker_thread, token)
     assert t == threading.current_thread()
+
+
+def test_BlockingTrioPortal_deprecated_export(recwarn):
+    import trio
+    btp = trio.BlockingTrioPortal
+    assert btp is BlockingTrioPortal