C#: Autosuggest in XMLDOCS suggests signatures that will not match after insertion when using nullable annotations with generics

_This issue has been moved from [a ticket on Developer Community](https://developercommunity.visualstudio.com/t/C:-Autosuggest-in-XMLDOCS-suggests-sign/10885507)._

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[severity:It's more difficult to complete my work]
Whenever you use a `cref="..."` attribute (be it inside a `<see ...>`/`<seealso ...` or `<inheritdoc ...>` tag in XMLDOCS you can get autosuggest suggestions that will **not** be recognized after insertion.

# Steps to reproduce:

1. Create a new C# project, be sure that `Nullable` is enabled.
2. Add any class.
3. Add a method and some xml documentation
```cs
/// <summary>
/// Foo
/// </summary>
public static void Foo<T>(T? foo) { }
```
4. Add _another_ method
```cs
public static void Bar() { }
```
5. Now try to inherit the second methods documentation from the first via `<inheritdoc cref="..." />`. As soon as you open the `cref` tag you will get an autosuggestion list.


6. **Pick** the "Foo" suggestion:

# Observation(s):
- _Note how the inserted signature inside the `cref` attribute is **white** and not **yellow** - yellow would mean a resolved signature, white is not_.
- _Note how the Intellisense documentation for the inheriting method is empty_:
- Enabling the "Documentation file" option for the project will fail to create documentation for the documentation inheriting method:

## Workaround:
You have to **manually** remove all `?` annotations inside the cref attribute for Intellisense to correctly resolve the referenced signature:

# Observed behaviour:
Code (xmldoc) completion suggestions produce signatures that cannot be resolved by Intellisense or the xmldoc compiler.

# Expected behaviour:
Code (xmldoc) completion suggestions should poduce signatures that can later be resolved by Intellisense/xmldoc compiler.

### Regression?
I *think* this might be a regression, but I'm not sure. I only particularly noticed this behaviour in the latest Version (17.13.5) of Visual Studio.

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### Original Comments

#### Feedback Bot on 4/7/2025, 00:24 AM:

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