Add support for SynExpr.Set(_,_,_)

[nojaf]

Description

There are a couple of warnings in the code base about not matching SynExpr.Set.

Repro code

let arr = [|0|]
(arr.[0]) <- 1

and

type T() =
    member val X = 0 with get, set
(T().X) <- 1

and

let mutable x = 0
(x) <- 1

do not produce output with 2.9.1.

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