Support "multi-session" mode properly

Document remote debugging and add a test

support/test/python/simple_python/.vimspector.json

@@ -2,7 +2,7 @@
   "configurations": {
     // This is a comment.
     "run legacy vscode-python": {
-      "adapter": "vscode-python" /* coment goes here too */,
+      "adapter": "vscode-python", /* coment goes here too */
       "configuration": {
         "request": "launch",
         "type": "python",
@@ -19,12 +19,9 @@
       }
     },
     "attach": {
-      "adapter": "debugpy",
+      "adapter": "multi-session",
       "configuration": {
-        "request": "attach",
-        "type": "python",
-        "host": "localhost",
-        "port": "5678"
+        "request": "attach"
       },
       "breakpoints": {
         "exception": {

support/test/python/simple_python/requirements.txt

@@ -1 +1 @@
-ptvsd==4.3.2
+debugpy

support/test/python/simple_python/run_with_debugpy

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+
+PYTHON=python3
+
+if [ -n "$1" ]; then
+  PYTHON=$1
+fi
+
+pushd $(dirname $0)
+  if [ -d env ]; then
+    rm -rf env
+  fi
+
+  $PYTHON -m venv env
+  . env/bin/activate
+  python -m pip install -r requirements.txt
+  echo "*** Launching ***"
+  python -m debugpy --wait-for-client --listen 0.0.0.0:5678 main.py
+popd
+

support/test/python/simple_python/run_with_ptvsd

@@ -1,19 +0,0 @@
-#!/usr/bin/env bash
-
-PYTHON=python3
-
-if [ -n "$1" ]; then
-  PYTHON=$1
-fi
-
-pushd $(dirname $0)
-  if [ ! -d env ]; then
-    virtualenv -p $PYTHON env
-  fi
-
-  . env/bin/activate
-  pip install -r requirements.txt
-
-  python -m ptvsd --wait --host localhost --port 5678 main.py
-popd
-