Was causing the following warning on Git checkout:
```
warning: the following paths have collided (e.g. case-sensitive paths
on a case-insensitive filesystem) and only one from the same
colliding group is in the working tree:
'packages/flutter_tools/test/data/vscode/application/Resources/app/package.json'
'packages/flutter_tools/test/data/vscode/application/resources/app/package.json'
```
VSCode installations on Linux appear to place the packages.json file at
`$VSCODE_INSTALL/resources/app/package.json` rather than at the expected
`$VSCODE_INSTALL/Resources/app/package.json`, causing the VSCode version
to not be reported correctly on Linux.
Fixes https://github.com/flutter/flutter/issues/169812
Looks in default install locations on Mac, Linux and Windows for VS Code. If found, looks in default extension location to see if Dart Code is installed.
If VS Code is not installed, nothing is reported. If VS Code is installed without Dart Code, a warning is shown.