Add disposedbeforeasyncrunanalyzer

[Smaug123]

We haven't got round to putting the analysers into the build pipeline for the service where this arose (I did one pass of fixing the analyser warnings, but I didn't merge the PR to add the analysers). I'm happy for us to get this into main and then enable the analysers on the pipeline and see in prod.

[Smaug123]

It occurs to me that this (from my above comment) is a good test case for when the analyser should not trigger:

let asyncReturningFunc () =
    do
        use t1 = new blah
        use t2 = new blah
        ()
    async {
        ...
    }

(similarly if we have a let-binding rather than a do)

In this case, it's clear and explicit that the disposables are disposed before the async is returned, let alone before it's run.

[dawedawe]

It occurs to me that this (from my above comment) is a good test case for when the analyser should not trigger:

Thanks, I added the use inside a do as another negative test. The let was already covered in another negative test.