Consider adding a `Clean Build` option with SPM

[compnerd]

Is your feature request related to a problem? Please describe.
When building with CMake, it is possible to do a clean build. This is not currently an option with the SPM based projects with VSCode.

Describe the solution you'd like
Having an additional build entry for Clean Build would allow you to do a full complete, clean build in a single invocation.

Describe alternatives you've considered
Running swift package clean before running the build task is a workaround.

Additional context

[adam-fowler]

If you right click in a Swift file the context menu has a Swift submenu which includes a clean build entry.

[plemarquand]

I think this would be best if left up to the extension user to define in their .vscode/tasks.json and/or .vscode/launch.json. This approach gives users the flexibility to tailor the order and specific commands run.

.vscode/tasks.json:

{
    "version": "2.0.0",
    "tasks": [
        {
            "label": "Swift: Clean Build Folder",
            "type": "shell",
            "command": "swift package clean",
            "group": "build"
        }
    ]
}

.vscode/launch.json:

{
    "version": "0.2.0",
    "configurations": [
        {
            "name": "Swift: Clean and Build",
            "type": "swift",
            "request": "launch",
            "program": "${workspaceFolder}/.build/debug/<program_name>"
            "preLaunchTask": "Swift: Clean Build Folder"
        }
    ],
    "tasks": {
        "version": "2.0.0",
        "tasks": [
            // Optionally define tasks here instead of tasks.json
        ]
    }
}