Support specifying additional tart launch arguments

[tonyarnold]

This PR proposes changes that allow the user to specify additional launch arguments for tart without using environment variables.

Description

• Add user-configurable Tart launch arguments: persisted in SettingsStore, editable in VM settings, and passed through VM start to Tart.
• Update VM start APIs and all call sites to accept arguments: [String].

Motivation and Context

The Simulator within my VMs has recently started asking for access to the microphone. I think it's simpler to disable audio input for the VM entirely, but to do that I need to pass arguments to tart when running the VM.

Ideally, there'd be a proper set of options and we could present a full UI for this, so consider this a first step on that path.

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)