WIP: Make multi-session debugging sort of work

This passes the session id around everywhere and ensures that things
like buffer names are all unique.

We now have the _vimspector_session update to point to the active (or
last accessed tab). This feels fairly natural and mostly seems to work.

NOTE: in vscode there is no "multiple tabs" - they actually add the
subprocesses to the stack trace somehow and when you click on a frame in
that it switches to the session for that process. Each process PC is
visible in the editor. It's kind of confusing.

Things still broken:
 - vimspector_session_windows
 - breakpoints need to be project-wide
 - PC display (how to show "all" PCs, or just show the current one for
   the current tab ?)
 - it would be nice for the tterminal buffers to be visible on all tabs.
   not sure how to do that.

support/test/python/multiprocessing/.vimspector.json

@@ -8,7 +8,26 @@
         "type": "python",
         "cwd": "${workspaceRoot}",
         "program": "${file}",
-        "stopOnEntry": false,
+        "stopOnEntry": true,
+        "console": "integratedTerminal",
+        "subProcess": true
+      },
+      "breakpoints": {
+        "exception": {
+          "raised": "N",
+          "uncaught": "Y",
+          "userUnhandled": ""
+        }
+      }
+    },
+    "attach": {
+      "adapter": "multi-session",
+      "configuration": {
+        "request": "attach",
+        "type": "python",
+        "cwd": "${workspaceRoot}",
+        "program": "${file}",
+        "stopOnEntry": true,
         "console": "integratedTerminal",
         "subProcess": true
       },

support/test/python/multiprocessing/multiprocessing_test.py

@@ -3,25 +3,16 @@ import multiprocessing as mp
 
 
 def First():
-  for _ in range( 100 ):
-    print( "in first" )
+  for i in range( 10 ):
+    print( f"in first x {i}" )
     time.sleep( 0.1 )
 
 
-def Second():
-  for _ in range( 100 ):
-    print( "in second" )
-    time.sleep( 0.1 )
+if __name__ == '__main__':
+  print( "main" )
+  p1 = mp.Process( target=First )
 
+  p1.start()
+  p1.join()
 
-print( "main" )
-p1 = mp.Process( target=First )
-p2 = mp.Process( target=Second )
-
-p1.start()
-p2.start()
-
-p1.join()
-p2.join()
-
-print( "Done" )
+  print( "Done" )