VSCode Troubleshooting

Following the instructions here: https://github.com/oae/asdf-flutter#troubleshooting

I tried adding `export FLUTTER_ROOT="$(asdf where flutter)"` to my `~/.zshrc` and restarted vscode, but couldn't get it to work.

I even tried setting `"terminal.integrated.automationProfile.osx"` for VSCode but that didn't help.
I also tried putting it in my `~/.bashrc` as well with the same results. I thought it worked once until I realized I opened the wrong repository :(

The only thing I could do to get it to work was setting VSCode settings with:
```
"dart.flutterSdkPaths": ["~/.asdf/installs/flutter/3.0.2"]
```
I did this at a workspace level so it isn't global, but I would to have a fix that works with any project without additional efforts. I also don't like that this now ultimately requires another location to update versions yet again that can be easily missed and cause headaches. Another problem I have with this is that this now should be committed to the repository and my personal get-around should not be in the repository, although asdf's `.tool-versions` should be in there, so this seems to be related close enough.

Start with the troubleshooting instructions in the repository README and reproduce the reported behavior using ~/.zshrc, ~/.bashrc, VSCode's terminal.integrated.automationProfile.osx, and dart.flutterSdkPaths. Investigate how the Flutter SDK selected by asdf and the repository's .tool-versions are exposed to VSCode; done means projects use the configured SDK without a workspace-specific path.

Written by the indexing model from the issue text.