isWatching/background task as preLaunchTask in launch.json

It would be nice to have a watcher task as preLaunchTask in launch.json. At the moment this is not possible because the launch task will not start before the preLaunchTask ends. A long running preLaunchTask should have a regex similar to problemMatcher to wait for a specific text in the output window before executing the launch task. In my scenario I’m running webpack dev server as a watcher task. I want this task to run if <kbd>F5</kbd> is hit and the preLaunchTask is not running. To delay the debugger launch it would be useful to test for a specific string in the output window webpack: bundle is now VALID.

[dbaeumer]

As mention the real fix is to allow something like

{
    "taskName": "abc",
    "background": {
         "activeOnStart": true,
         "beginsPattern": "^webpack: Compiling\\.\\.\\.$",
         "endsPattern": "^webpack: Compiled successfully\\.$"
    }
}

[dbaeumer]

We should support defining watch begin / end pattern without a problem pattern as well.