Switch expressions don't exaustevely check for local functions that return exceptions.

I tried to make the following code with switch expression.

```dart
static FirebaseOptions forPlatform({FirebaseOptions? android, FirebaseOptions? ios}) {
void throwUnsupportedPlatform(TargetPlatform platform) => throw UnsupportedError('DefaultFirebaseOptions are not supported for $platform.');

return switch (defaultTargetPlatform) {
TargetPlatform.android => android ?? throwUnsupportedPlatform(defaultTargetPlatform),
TargetPlatform.iOS => ios ?? throwUnsupportedPlatform(defaultTargetPlatform),
_ => throwUnsupportedPlatform(defaultTargetPlatform),
};
}
```

The analyzer complains that `A value of type 'void' can't be returned from the method 'forPlatform' because it has a return type of 'FirebaseOptions'.`. I imagined the analyzer would be able to know that `throwUnsupportedPlatform` always throws, so this is valid code.

This code works:

```dart
return switch (defaultTargetPlatform) {
TargetPlatform.android => android ?? (throw UnsupportedError('DefaultFirebaseOptions are not supported for $defaultTargetPlatform.')),
TargetPlatform.iOS => ios ?? (throw UnsupportedError('DefaultFirebaseOptions are not supported for $defaultTargetPlatform.')),
_ => throw UnsupportedError('DefaultFirebaseOptions are not supported for $defaultTargetPlatform.'),
};
```

Start by reproducing the reported switch-expression example and compare it with the version that throws inline. Trace how the analyzer types a local function declared to return void, then identify the language or analyzer behavior that should recognize an always-throwing function. Done means the example is accepted without weakening return-type checking, with coverage for both switch-expression branches and the existing inline-throw behavior.

Written by the indexing model from the issue text.