Categorise things like SDK paths as machine-specific #1717
Description
https://code.visualstudio.com/updates/v1_34#_machinespecific-settings
Otherwise we'll get weird issues running on containers because local paths are passed in:
ERR EINVAL: invalid argument, open '/workspaces/vscode-dev-containers/containers/flutter/M:\Coding\Applications\Dart-Code-Logs\insiders.analyzer.txt': Error: EINVAL: invalid argument, open '/workspaces/vscode-dev-containers/containers/flutter/M:\Coding\Applications\Dart-Code-Logs\insiders.analyzer.txt'