Issue description

Consider

type DU = MyCase of (string 
                        | // but why?
                            null)

Without having the range of |, we can't link the comment to the correct syntax node in Fantomas.
Would be great if we could have the range in the AST.

https://fsharp.github.io/fsharp-compiler-docs/reference/fsharp-compiler-syntax-syntype.html#WithNull

Choose one or more from the following categories of impact

• Unexpected nullness warning (false positive in nullness checking, code uses --checknulls and langversion:preview).
• Missing nullness warning in a case which can produce nulls (false negative, code uses --checknulls and langversion:preview).
• Breaking change related to older null constructs in code not using the checknulls switch.
• Breaking change related to generic code and explicit type constraints (null, not null).
• Type inference issue (i.e. code worked without type annotations before, and applying the --checknulls enforces type annotations).
• C#/F# interop issue related to nullness metadata.
• Other (none of the categories above apply).

Operating System

Windows (Default)

What .NET runtime/SDK kind are you seeing the issue on

.NET SDK (.NET Core, .NET 5+)

.NET Runtime/SDK version

FCS 43.9.100-preview.24422.2

Reproducible code snippet and actual behavior

type DU = MyCase of (string 
                        | // but why?
                            null)

Possible workarounds

No response