Improve the check for whether a project is Flutter to be more reliable #4702
Description
This code does a basic regex to check for sdk: flutter in the pubspec.yaml to decide whether a project is a Flutter project or not:
Dart-Code/src/shared/utils/fs.ts
Lines 141 to 144 in b7c1124
It was done this way for simplicity when we had no yaml parser referenced. It can be tripped up by comments and other unrelated keys. Now we have a yaml parser, we should do this properly so it's reliable.