Add "," as separator for pattern matching on multiple named discriminated unions fields and deprecate ";"

# Make it possible to deconstruct multi-field Discriminated Unions by naming multiple fields

Right above https://docs.microsoft.com/en-us/dotnet/fsharp/language-reference/discriminated-unions#unwrapping-discriminated-unions, it is documented that we can match a discriminated unions by a single field name.

```fs
type Shape =
| Rectangle of width : float * length : float
| Circle of radius : float
| Prism of width : float * float * height : float

let getShapeWidth shape =
match shape with
| Rectangle(width = w) -> w
| Circle(radius = r) -> 2. * r
| Prism(width = w) -> w
```

However, as soon as we try to match more than one field,
```fs
let getContainedSpace shape =
match shape with
| Rectangle(w, l) -> w * l
| Circle(r) -> System.Math.PI * r ** 2.
| Prism(w, l, height = h) -> w * l * h // The "height = " causes these errors
// error FS0010: Unexpected symbol '=' in pattern. Expected ')' or other token.
// error FS0583: Unmatched '('
// error FS0010: Unexpected symbol '=' in pattern. Expected ')' or other token.
// error FS0583: Unmatched '('
// error FS0039: The value or constructor 'h' is not defined.
```
This feature is so incomplete!

## Pros and Cons

The advantages of making this adjustment to F# are
1. Extending an existing feature to satisfy more use cases
2. More consistency between constructing and deconstructing a discriminated union. This is already allowed for the construction side.

The disadvantages of making this adjustment to F# are (none)

## Extra information

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

Related suggestions: (put links to related suggestions here)

## Affidavit (please submit!)

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

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