Generic equality should use the `SetEquals` method

**I propose we** ... (describe your suggestion here)

In .net runtime, there are many Set types that all have `SetEquals` methods. Generic equality should use the `SetEquals` method.

```fsharp
let x = HashSet [1;2;3]
let y = HashSet [1;2;3]
Console.WriteLine($"{x=y}") // false
Console.WriteLine($"{x.SetEquals y}") // true
```

**The existing way of approaching this problem in F# is** ...

## Pros and Cons

**The advantages of making this adjustment to F# are** ...

**The disadvantages of making this adjustment to F# are** ...

## Extra information

**Estimated cost (XS, S, M, L, XL, XXL):**

**Related suggestions:** (put links to related suggestions here)

## Affidavit (please submit!)

Please tick these items by placing a cross in the box:
* [ ] This is not a question (e.g. like one you might ask on [StackOverflow](http://stackoverflow.com)) and I have searched StackOverflow for discussions of this issue
* [ ] This is a language change and not purely a tooling change (e.g. compiler bug, editor support, warning/error messages, new warning, non-breaking optimisation) belonging to [the compiler and tooling repository](https://github.com/dotnet/fsharp)
* [ ] This is not something which has obviously "already been decided" in previous versions of F#. If you're questioning a fundamental design decision that has obviously already been taken (e.g. "Make F# untyped") then please don't submit it
* [ ] I have [searched both open and closed suggestions on this site](http://github.com/fsharp/fslang-suggestions/issues) and believe this is not a duplicate

Please tick all that apply:
* [ ] This is not a breaking change to the F# language design
* [ ] I or my company would be willing to help implement and/or test this

## For Readers

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No source files, tests, or entry points are named. Start by reviewing the proposal and its HashSet/SetEquals example, then determine the intended generic-equality semantics, affected language or runtime behavior, and tests needed to show the change is complete.

Written by the indexing model from the issue text.