Update launch.json schema to add "qt"

[int19h]

This controls whether the debugger monkey-patches PyQt/PySide to detect and trace Qt threads (microsoft/debugpy#308).

Valid values are:

• "auto"
• "none"
• "pyside"
• "pyside2"
• "pyqt4"
• "pyqt5"

The default is "auto", which tries to auto-detect this by import probing - this is the same as ptvsd 4 behavior.

Since that heuristic may be wrong if several different packages are installed side-by-side, the ability to specify the desired one explicitly is also provided.

"none" is provided, to give the users the ability to opt out of monkey-patching in case it breaks something.

[karthiknadig]

/cc @luabud for the defaults and text.

[lucs100]

This doesn't seem to support PyQt6 - the only way I could get breakpoints to trigger in a thread's run method was to manually add debugpy.debug_this_thread(). "pyqt6" isn't a valid value for the "qt" field; when setting "qt": "pyqt6" in my launch configs I get the error:

couldn't handle #1 request "launch" from Adapter:
             Invalid message: "qt" must be one of: ['none', 'auto', 'pyside', 'pyside2', 'pyqt4', 'pyqt5']```

[brettcannon]

Due to limited resources and lack of general interest, we are unfortunately closing this issue.