Resolve `<see cref>` in XML doc comments like C#

[xperiandri]

Is your feature request related to a problem? Please describe.

<see cref="…"/>, <seealso cref>, <exception cref> and <permission cref> in F# /// comments are plain text to the compiler and the IDE:

• --doc copies the attribute verbatim (XmlDocFileWriter.WriteXmlDocFile), so <see cref="Parse"/> reaches the .xml file as Parse. C# writes the documentation ID (M:Ns.Parser.Parse(System.String)), and tools that read the file (DocFX, fsdocs, Visual Studio tooltips of the consuming project) resolve IDs, not source names. The unresolved-cref diagnostic already exists (xmlDocUnresolvedCrossReference, FS3390 group) but is never raised.
• In the editor, a cref is not a symbol: Go To Definition does nothing on it, renaming the type or member leaves it stale, and the tooltip prints the raw text.

Describe the solution you'd like

The same as C#, built on the XML doc ranges from #20637:

1. The checker resolves each cref against the file's final environment (so it can point forward, as in C#): the enclosing type's members first, then values, types and modules — the nameof resolution order. A resolved cref is reported as a related symbol use of a new kind (RelatedSymbolUseKind.XmlDocCref), opt-in like XmlDocParameter in Report XML doc parameter names as related symbol uses #20637, so symbol search is not bloated.
2. --doc writes the documentation ID of the resolved symbol; an unresolved cref is written as !:Text and reported under FS3390. A cref that already carries a prefix (T:, M:, …) is kept as is.
3. The editor: Rename rewrites the last segment of the cref (Rename a parameter together with its XML doc param tags #20638 already passes all related kinds to Rename), Go To Definition works on it, and the tooltip shows the resolved name.

A first cut would cover types, modules, union cases, fields, properties, events and non-overloaded methods, and leave M(int) overload syntax, List{T} generics and operators for later.

Describe alternatives you've considered

• Resolving where each doc comment is converted: a type's doc is converted before the rest of its recursive group and its members exist, so forward references would not resolve.
• Producing the IDs during checking: XmlDocSigOfVal needs the generalized type and ValReprInfo, and the IDs are cached on the Val; they have to be made when --doc writes the file.

Additional context

Questions before any code:

1. Should Find All References list crefs? C# does; Report XML doc parameter names as related symbol uses #20637/Rename a parameter together with its XML doc param tags #20638 keep <param> names out of it.
2. Is rewriting the .xml output a compiler change that can go in behind --doc, or does it need a language suggestion first?
3. Should FS3390 for an unresolved cref stay opt-in, like the rest of that warning?

Related: #20630, #20637, #20638, #15134, #20591.