Simplify generated launch.json

Hey,

VSCode dev here. This milestone I am looking into simplifing generated launch.json for various extensions Microsoft/vscode#62851

The launch.json that C++ generates is attached at the end. I suggest to simplify it the following way:

• DebugConfigurationProvider should use the quickPick to ask the user if he would like to launch or attach. After that for the program name. Optimally it should be able to detect those things on its own, but if not possible use quickPick to ask the user.
• Remove default fields which are not necessery like cwd, stopAtEntry, args, 'environment'
• Do users ever change MIMode/ If no than this property should be append in the resolveConfiguraiton calls. That way the user will not see any of this and there will be far less clutter
• You are already contributing snippets to launch.json, but not using the configuraitonSnippets field in the package.json. Why is that? Also these snippets could be simplified

If you agree with the suggestions I am making here I am also here to help with any potential questions you might have. The changes should not require a lot of work but will simplify the flow a lot imho. It should be much less complex and not too much like a wizard experience

{
    // Use IntelliSense to learn about possible attributes.
    // Hover to view descriptions of existing attributes.
    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
    "version": "0.2.0",
    "configurations": [
        {
            "name": "(lldb) Launch",
            "type": "cppdbg",
            "request": "launch",
            "program": "enter program name, for example ${workspaceFolder}/a.out",
            "args": [],
            "stopAtEntry": false,
            "cwd": "${workspaceFolder}",
            "environment": [],
            "externalConsole": true,
            "MIMode": "lldb"
        }
    ]
}

Start with the DebugConfigurationProvider and its resolveConfiguration calls, then inspect package.json for configurationSnippets. Review how launch.json is currently generated, including the launch/attach and program prompts and default fields. Done means the generated configuration and snippets are simpler while preserving the required launch behavior.