[Repo Assist] Fix GetNestedType on generic provided type symbols (issue #336)

[github-actions]

🤖 This PR was created by Repo Assist, an automated AI assistant. Fixes #336.

Problem

FSharpType.GetUnionCases (and any code that calls GetNestedType) would throw a NotSupportedException when called on a type created with ProvidedTypeBuilder.MakeGenericType where at least one type argument is a provided type. For example:

let typ = ProvidedTypeDefinition("Blah", Some typeof(obj))
let optionTyp = ProvidedTypeBuilder.MakeGenericType(typedefof<_ option>, [ typ ])
// ↑ This is TypeSymbol(OtherGeneric(typedefof<_ option>), [typ])

let cases = FSharp.Reflection.FSharpType.GetUnionCases(optionTyp)
// ↑ Throws: "The operation 'GetNestedType' on item 'FSharpOption`1' should not be called
//   on provided type, member or parameter of type 'TypeSymbol'"

Root cause

ProvidedTypeBuilder.MakeGenericType(typedefof<_ option>, [someProvidedType]) produces a TypeSymbol with TypeSymbolKind.OtherGeneric. Its GetNestedType override unconditionally called notRequired, even though the underlying generic type definition (FSharpOption(T)) is a real .NET type that supports GetNestedType.

Separately, ProvidedTypeSymbol (used when the generic type definition itself is a provided type) had the same gap.

Fix

Delegate GetNestedType to the underlying generic type definition for both cases — exactly the same pattern already used by GetNestedTypes at the same sites.

// TypeSymbol (OtherGeneric path)
override this.GetNestedType(name, bindingFlags) =
    match kind with
    | TypeSymbolKind.OtherGeneric gtd -> gtd.GetNestedType(name, bindingFlags)
    | _ -> notRequired this "GetNestedType" this.Name

// ProvidedTypeSymbol (Generic path)
override this.GetNestedType(name, bindingFlags) =
    match kind with
    | ProvidedTypeSymbolKind.Generic gty -> gty.GetNestedType(name, bindingFlags)
    | _ -> notRequired this "GetNestedType" this.FullName

Test status

✅ New regression test GetUnionCases works on option of provided type passes.
✅ All 103 existing tests pass, 1 pre-existing skip unchanged (dotnet test tests/ -c Release).

Generated by Repo Assist for issue #336

Generated by Repo Assist

To install this agentic workflow, run

gh aw add githubnext/agentics/workflows/repo-assist.md@69c1ee19e39e6aaba35519aafefb5cbf314de323