Reject non-function bindings for single-case and partial active pattern names

[Copilot]

The compiler previously rejected non-function multi-case active patterns ((|A|B|)) but still allowed equivalent invalid forms for single-case ((|A|)) and partial ((|A|_|)) names. This left declarations that tooling recognized as active patterns but could not be used in pattern positions.

• Checker behavior aligned across active pattern forms

  • Updated post-inference active-pattern validation to run the function-typed check for all active pattern bindings, not only multi-case ones.
  • This makes FS1209 (Active pattern '...' is not a function) consistently apply to single-case and partial declarations as well.

• Conformance coverage expanded

  • Extended E_ActivePatternNotAFunction.fs with explicit single-case and partial non-function declarations.
  • Updated expected diagnostics in Named.fs to assert all three FS1209 errors.

• Example of newly-rejected declarations

  let (|C|) = 3
  let (|D|_|) = None
  // now reported as FS1209: Active pattern '...' is not a function

[github-actions]

❗ Release notes required

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✅ Found changes and release notes in following paths:

Change path	Release notes path	Description
src/Compiler	docs/release-notes/.FSharp.Compiler.Service/11.0.100.md