Rule/Perf: Reduce allocations in no-floating-promises

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Suggestion

In no-floating-promises, every ExpressionStatement invokes isUnhandledPromise, which recursively walks the tree. As it does, it reports information in the form of an object. These objects contain up to 3 boolean properties which are not always set.

    function isUnhandledPromise(
      checker: ts.TypeChecker,
      node: TSESTree.Node,
    ): {
      isUnhandled: boolean;
      nonFunctionHandler?: boolean;
      promiseArray?: boolean;
    }

I have not measured the cost yet, but instead of returning a new object with varying shapes, I figured these could be represented as bit flags on a small int.

Additional Info

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