Enable embedded vim python debugging

This allows us to use vimspector to debug vimspector. The idea is that
in Vim you call 'py3 from vimspector.developer import SetUpDebugpy;
SetUpDebugpy()' and then just attach to localhost:5678 using the new
multi-session mode support. Oof.

.vimspector.json

@@ -0,0 +1,14 @@
+{
+  "configurations": {
+    "Python: Attach To Vim": {
+      "variables": {
+        "port": "5678",
+        "host": "localhost"
+      },
+      "adapter": "multi-session",
+      "configuration": {
+        "request": "attach"
+      }
+    }
+  }
+}