[Bug] .NET API bug with ValueTuple handling

[Aragas]

Describe the bug
ValueTuple brings some unexpected behaviour for DocFX reference API generation.
DocFX does ReferenceItem merging, but when the ValueTuple is not default - has custom named symbol names

[return: TupleElementNames(new string[] { "name", "value" })]
ValueTuple<string, int> GetCompanionWithMostKills();

So instead on an unnamed ValueTuple (string, int) we got string name, int item.
This breaks two asserts

docfx/src/Microsoft.DocAsCode.Dotnet/ExtractMetadata/ReferenceItem.cs

Line 134 in 6b81b48

Debug.Assert(sourceParts.Count == targetParts.Count);

docfx/src/Microsoft.DocAsCode.Dotnet/ExtractMetadata/ReferenceItem.cs

Line 140 in 6b81b48

Debug.Assert(sourceParts[i].Name == targetParts[i].Name);

The first one breaks because there are now additional NameParts, the second breaks because for the same ValueTuple signature there can exist different name pairs (string something_else, int something_else2)

To Reproduce
Steps to reproduce the behavior:
Have a signature like

[return: TupleElementNames(new string[] { "name", "value" })]
ValueTuple<string, int> GetCompanionWithMostKills();
[return: TupleElementNames(new string[] { "name", "value2" })]
ValueTuple<string, int> GetCompanionWithMostElse();

Expected behavior
I didn't check the consequences, but I assume it might fail to correctly show the custom parameter names in some cases

Context (please complete the following information):

• OS: Windows

• Docfx version: 2.66.2

• .NET version: .NET 7.0

• docfx.json config:
  Not needed

• Exceptions
  Not needed

• Errors and warnings
  Not needed

• .NET info
  Not needed

Additional context
Not needed

[yufeih]

Display of returns would be wrong, due to how docfx today stores and renders type signatures.