Add --allow-file-access-from-files to default runtime arguments ... in trusted workspaces

[GitMensch]

Reasoning: This is an extension for developers which will open local files - of course these should be able to include local files...
See https://stackoverflow.com/questions/4558160/xsl-not-working-in-google-chrome for some details (and the reason that this is not the default in chrome, as it also isn't in firefox).

As vscode introduced the trusted workspace concept it seems very reasonable to always add this option in trusted workspaces, while leaving it out otherwise. This is also the core difference to #77 (which would be "only if the user specified, and then always).