Consider adding unnecessary_statements to the recommended set

[DanTup]

I was asked today by a new Dart developer why his code didn't produce any diagnostics when he'd missed the () from the end of a method call:

state.foo;

This isn't the first time this has come up to me, and it's also been asked for in the SDK. It seems like a useful lint and it seems like the false positives are real edge cases (like side effects in operators) so I wonder if it would be useful to recommend?

Some issues requesting this (or issues that it may have been avoided if it was used):

• [linter] adding unnecessary_statements to the "recommended rule set" sdk#59732
• proposal: alert me when I forget method's brackets sdk#58725
• Prevent equality checks as statements sdk#59028
• Would like a lint to handle unused tearoffs (or similar) sdk#57760
• [Suggestion]: Flag statements of the form: x == y; as "statement yields unused boolean" sdk#58484
• Unused boolean statements sdk#57319
• Warning if a function call is missing parenthesis sdk#58281
• Hint about statements with no effect sdk#18849
• Analyzer should lint if a statement consists of only an == expression sdk#30793

Additionally, it is enabled in the Flutter repository:

• https://github.com/flutter/flutter/blob/188d1e1999c7dd2804d3802976248fdad12d4372/analysis_options.yaml#L236

Possible false positives I can find are all related to operators with side effects (which I think is probably acceptable - I don't think this is common, except perhaps while print-debugging!):

• False positive: unnecessary_statements sdk#57964
• unnecessary_statements shouldn't trigger when the operator is overloaded sdk#59188