[vscode] Debug setup work should use vscode extensions instead of shell scripts

[danieljurek]

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From discussions in https://github.com/Azure/azure-dev/issues/370

Web debug should work by clicking "play"

• Insert a hosted url value in launch.json (in codespaces) or localhost:3000

• Implement a task which can run commands like the Web npm start task, but with a dotenv file (location dynamically determined). This task would need to use matchers so that it could pass control back to the task system.

• Implement a teardown task which ends tasks associated with a debug run. After debugging ends the task would end associated tasks that initiated the run.