Document stopAllThreadsOnSuspend launch option and add it to the launch.json schema #1133

With the pre-release Python Debugger extension, the stopAllThreadsOnSuspend launch option is honored by debugpy (presumably via the vendored pydevd 3.5.0, #2010 in microsoft/debugpy), but it is not documented and VS Code flags it as an unknown property in launch.json.

With this configuration, when a breakpoint is hit, only the thread that hit it is suspended; other threads keep running:

  "type": "debugpy",
  "request": "launch",
  "module": "my_module",
  "steppingResumesAllThreads": false,
  "stopAllThreadsOnSuspend": false
}

Without the option, all threads are suspended (the long-standing default).

Why this matters

When testing systems, background threads must keep running while a test thread is paused. Otherwise, connections time out and the device state becomes invalid.

Request

Confirm that stopAllThreadsOnSuspend (and steppingResumesAllThreads) are supported debugpy options.
Add them to the launch.json schema, so VS Code no longer reports them as unknown.
Document them, including the debugpy defaults. Proposed text:
stopAllThreadsOnSuspend: when true (default), all threads are suspended when a breakpoint is hit or the program is paused. When false, only the thread that triggered the stop is suspended.
steppingResumesAllThreads: when true (default), all threads are resumed during a step operation. When false, only the current thread is resumed.