Add new vscode command to show ast

[felix-andreas]

• Add a new vscode command: Roughly: Show Syntax Tree -> this opens a new virtual document with the same output as cli roughly debug ast. Therefore you can use tree::format
• write reasonable amount of tests if possible
• only write comment if impdroves clarity (use similar amounts of comments as in other files)
• orient on current code style (keep it functional -> bend don't bend backwards just to be functional)