* Update VS Code validator to match Android Studio
- Now shows a tick (instead of partial) if installed
- Now shows a cross (instead of dot) if extension is not installed
Fixes#22931.
It's not usual for this not to be set, but it affected at least one user (#23909) and there are a non-zero number of people online saying it's not set. It's better that we don't crash.
Fixes#23909.
* Fixes resulting from audit of issues links
I looked at every link to GitHub in our repo. For cases where we had a TODO that was waiting for a bug to be fixed, and the bug has now been fixed, I applied the pending change. For cases where the link was out of date, I updated the link.
* Update run_test.dart
skip this test again since it failed on linux and macos bots
Seems like VS Code may have started using lowercase extension folders recently (our identifier is `Dart-Code.flutter` but now the folder is named `dart-code.flutter`), so this makes the check not sensitive to casing.
Also reuse extension identifier for download link
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.
