Renaming a parameter does not update `<param>`, `<paramref>`, `<typeparam>` and `<typeparamref>` in its XML doc

[xperiandri]

/// <summary>Adds two numbers.</summary>
/// <typeparam name="T">The number type.</typeparam>
/// <param name="x">The first number.</param>
/// <param name="y">Added to <paramref name="x"/>.</param>
let add<'T when 'T :> System.Numerics.INumber<'T>> (x: 'T) (y: 'T) = x + y

Renaming x (F2 in Visual Studio) rewrites the parameter and its uses in the body, but leaves name="x" in both <param> and <paramref> untouched, so the doc now documents a parameter that no longer exists. Renaming 'T likewise leaves <typeparam name="T"> behind.

Expected: the rename also updates the name attribute of every <param>, <paramref>, <typeparam> and <typeparamref> that refers to the renamed parameter, as it does in C#. This applies to let-bound functions, members, primary constructors and union case fields, and to type parameters.

Two things to keep in mind for the fix:

• The compiler does not know where name="x" sits in the source: PreXmlDoc.ToXmlDoc merges the per-line ranges of the /// lines into one, and FS3390 reports on the whole block. This is what Have PreXmlDoc/XmlDoc track names and ranges for param/paramref children #15134 asks to change.
• The new text differs from the code: 'T renamed to 'U must become U in name="U", and a backticked name must be written without the backticks.

Related: #15134

[xperiandri]

@T-Gro should the fix be placed into the compiler or into the editor?

[xperiandri]

Compiler side: keep the per-line ranges in XmlDoc (today PreXmlDoc.ToXmlDoc merges them) and report each name="x" to the name-resolution sink as a use of the parameter. That would give rename, Find All References and highlighting in VS, FSAC and Rider for free, and close #15134. The cost is a change in the checker plus a filter so that semantic classification does not colour text inside comments, and there is no precedent for reporting ranges inside comments.

Editor side: after the FCS locations are collected, find the owning binding or constructor in the parse tree and scan its /// block for name="x" in the four tags. That is a small PR with no FCS API change, but it only helps rename in VS, so Find All References, highlighting and other clients stay blind. In both cases rename needs a small editor step to write U for a renamed 'U and to drop backticks from an escaped name.

[T-Gro]

We had a sibling issue asking for enriching the data stored for xml docs - since paramnames are being checked, their ranges could be also stored.

(that storage and processing would belong to the compiler side).

Even though rename cooperation makes sense, rename is powered by finding references and any change should make sure to not bloat the symbol search with xmldoc results.