Value on DocId's MemberSignature tag does not match with corefx's member name when referring an innner class of a generic-type class.

The name of members in xml files in corefx/artifacts/bin folder, generated from triple-slash comments within the source code does not match the dotnet-api-docs/xml ``'s value when it references an inner class within a generic class.

Take the following signature as an example:
```
public static ImmutableArray ToImmutableArray(this ImmutableArray.Builder builder)
```
This signature recieves a param of the type `ImmutableArray.Builder `, which is a class defined within the `ImmutableArray` class.
This signature is converted to the following values.

on corefx\artifacts\bin\System.Collections.Immutable\netcoreapp-Debug\System.Collections.Immutable.xml:
```

```
on dotnet-api-docs\xml\System.Collections.Immutable\ImmutableArray.xml:
```

```

As you can see, there is a difference in the `Value` of both nodes property, right in the parameter type.

This is affecting us because we were automatically porting APIs documented via triple-slash comments to the docs repo, with this difference we are unable to match the APIs and we need to go and manually copy-paste the info in the source to the docs repo.

In addition, in the [docs page](https://docs.microsoft.com/en-us/dotnet/api/system.collections.immutable.immutablearray.toimmutablearray?view=netcore-3.0#System_Collections_Immutable_ImmutableArray_ToImmutableArray__1_System_Collections_Immutable_ImmutableArray___0__Builder_) you can see that the name of the overload says that it expects a `ImmutableArray` when it should say `ImmutableArray.Builder`.