Better error reporting for let bindings.

[edgarfgp]

Description

• Updates TcNormalizedBinding to use the SynPat range to show more accurate error ranges.

Before

[<VolatileField>]
^^^^^^^^^^^^^^^^^
let mutable x = 6
^^^^^^^^^^^^^^

After

[<VolatileField>]
let mutable x = 6
            ^

• Adds a new compiler error for Multi-case partial active patterns

Before

We just showed an unclear error message that did not make it clear that multi-case partial active patterns are not supported.

let (|A|B|_|) = None  // FS0827: This is not a valid name for an active pattern

After

let (|A|B|_|) = None  // FS3872: Multi-case partial active patterns are not supported. Consider using a single-case partial active pattern or a full active pattern.

• Updates FS0827 to include the active pattern's name

Before

FS0827: This is not a valid name for an active pattern

After

FS0827: (|A|B|)' is not a valid method name. Use a 'let' binding instead.

Checklist

• Test cases added
• Release notes entry updated

[github-actions]

❗ Release notes required

---

✅ Found changes and release notes in following paths:

Change path	Release notes path	Description
src/Compiler	docs/release-notes/.FSharp.Compiler.Service/9.0.100.md

[edgarfgp]

@psfinaki Thanks a lot for the help. You are a Legend. Will be updating the PR description soon to cover and explain all the goodness here :)

[vzarytovskii]

@psfinaki @T-Gro @abonie please review, we will have to either merge it soon, or wait until after 9.0.100 release, since SDK freeze is soon (in couple of weeks), and we will need to merge it and wait for translations.

[psfinaki]

I this this is in the good shape, thanks Edgar!