Throw a StateError if ResourceHandle.to* is called more than once. #49878
Description
Change
Throw a StateError if ResourceHandle.toFile(), ResourceHandle.toSocket(), ResourceHandle.toRawSocket() or ResourceHandle.toRawDatagramSocket() is called more than once.
Rationale
Calling ResourceHandle.toFile(), ResourceHandle.toSocket(), ResourceHandle.toRawSocket() or ResourceHandle.toRawDatagramSocket() more than once produces two distinct Dart objects that are backed by the same file descriptor, which will become invalid when one object is closed or GCed.
For example:
void main(List<String> args) async {
final executeInternalCommand = DynamicLibrary.process().lookupFunction<
Void Function(Pointer<Char>, Pointer<Void>),
void Function(
Pointer<Char>, Pointer<Void>)>('Dart_ExecuteInternalCommand');
final gcNow = "gc-now".toNativeUtf8();
final file = File('/tmp/file.txt');
await file.create();
final openFile = await file.open();
final handle = ResourceHandle.fromFile(openFile);
handle.toFile().writeStringSync('test');
executeInternalCommand(gcNow.cast(), nullptr); // Will collect the file produced by `toFile` .
handle.toFile().writeStringSync('test'); // Error because the file descriptor is no longer valid.
}Impact
It is unlikely that this will break any existing correct code.
Mitigation
Users can save the result of the ResourceHandle.toFile(), etc. and use that instead of calling ResourceHandle.toFile() again.