[Bug] It is not possible to use the `cref` attribute with the DocAsCode.App package.

**Describe the bug**
[Microsoft.DocAsCode.App](https://www.nuget.org/packages/Microsoft.DocAsCode.App) ignores the documentation when the `cref` attribute is used.

**To Reproduce**
Create an example class with XML documentation using the `cref` attribute:
```cs
namespace src;

public class ExampleClass
{
///
/// Test .
///
/// InvalidOperationException
/// ArgumentNullException
public void Foo()
{

}
}
```
**Note:** Use Implicit Usings.

**Expected behavior**

**Context (please complete the following information):**
- OS: Windows
- Docfx version: 2.60.2
- .NET version: .NET 7.0

- `docfx.json` config

```json
{
"metadata": [
{
"src": [
{
"files": [
"src/**.csproj"
]
}
],
"dest": "api",
"disableGitFeatures": false,
"disableDefaultFilter": false
}
],
"build": {
"content": [
{
"files": [
"api/**.yml",
"api/index.md"
]
},
{
"files": [
"articles/**.md",
"articles/**/toc.yml",
"toc.yml",
"*.md"
]
}
],
"resource": [
{
"files": [
"images/**"
]
}
],
"overwrite": [
{
"files": [
"apidoc/**.md"
],
"exclude": [
"obj/**",
"_site/**"
]
}
],
"dest": "_site",
"globalMetadataFiles": [],
"fileMetadataFiles": [],
"template": [
"default"
],
"postProcessors": [],
"markdownEngineName": "markdig",
"noLangKeyword": false,
"keepFileLink": false,
"cleanupCacheHistory": false,
"disableGitFeatures": false,
"xrefService": [ "https://xref.docs.microsoft.com/query?uid={uid}" ]
}
}
```

- Errors and warnings

```csharp
Build succeeded with warning.
[23-01-21 08:36:07.244]Warning:[ExtractMetadata]Invalid cref value "!:System.InvalidOperationException" found in triple-slash-comments for Foo defined in src/ExampleClass.cs Line 9, ignored.
[23-01-21 08:36:07.245]Warning:[ExtractMetadata]Invalid cref value "!:System.InvalidOperationException" found in triple-slash-comments for Foo defined in src/ExampleClass.cs Line 9, ignored.
[23-01-21 08:36:07.245]Warning:[ExtractMetadata]Invalid cref value "!:System.ArgumentNullException" found in triple-slash-comments for Foo defined in src/ExampleClass.cs Line 9, ignored.
3 Warning(s)
0 Error(s)
```

- .NET info

```csharp
SDK DE .NET:
Version: 7.0.102

Entorno de tiempo de ejecución:
OS Name: Windows
OS Version: 10.0.19045
OS Platform: Windows
RID: win10-x64
Base Path: C:\Program Files\dotnet\sdk\7.0.102\

Host:
Version: 7.0.2
Architecture: x64
Commit: d037e070eb

.NET SDKs installed:
3.1.426 [C:\Program Files\dotnet\sdk]
5.0.104 [C:\Program Files\dotnet\sdk]
5.0.303 [C:\Program Files\dotnet\sdk]
6.0.113 [C:\Program Files\dotnet\sdk]
7.0.100 [C:\Program Files\dotnet\sdk]
7.0.102 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
Microsoft.AspNetCore.App 3.1.31 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 3.1.32 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.9 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 6.0.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 7.0.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 7.0.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
Microsoft.NETCore.App 3.1.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.31 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 3.1.32 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.4 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 6.0.13 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.2 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
Microsoft.WindowsDesktop.App 3.1.8 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.31 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 3.1.32 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 5.0.4 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 5.0.9 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.11 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 6.0.13 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 7.0.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
Microsoft.WindowsDesktop.App 7.0.2 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
```

**Additional context**
These warnings do not happen with DocFX version 2.59.4.0 (without using **Implicit Usings**).