C# code generation generates invalid code when accessing UDT items named `Data`.

[cgranade]

Describe the bug

When a UDT has a named item whose name is Data, accessing that item causes C# code generation to display a warning:

Microsoft (R) Build Engine version 16.3.0-preview-19377-01+dd8019d9e for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

  Restore completed in 23.26 ms for C:\Users\<redacted>\tmp\runtime-bug\runtime-bug.csproj.
  You are using a preview version of .NET Core. See: https://aka.ms/dotnet-core-preview
obj\qsharp\src\Operations.g.cs(27,31): warning CS0108: 'Foo.Data' hides inherited member 'QTuple<IQArray<long>>.Data'. Use the new keyword if hiding was intended. [C:\Users\<redacted>\tmp\runtime-bug\runtime-bug.csproj]
  runtime-bug -> C:\Users\<redacted>\tmp\runtime-bug\bin\Debug\netcoreapp2.1\runtime-bug.dll

If the UDT contains named items other than Data as well, then the code generation step fails entirely:

Microsoft (R) Build Engine version 16.3.0-preview-19377-01+dd8019d9e for .NET Core
Copyright (C) Microsoft Corporation. All rights reserved.

  Restore completed in 24.7 ms for C:\Users\<redacted>\tmp\runtime-bug\runtime-bug.csproj.
  You are using a preview version of .NET Core. See: https://aka.ms/dotnet-core-preview
obj\qsharp\src\Operations.g.cs(27,31): warning CS0108: 'Foo.Data' hides inherited member 'QTuple<(IQArray<long>, string)>.Data'. Use the new keyword if hiding was intended. [C:\Users\<redacted>\tmp\runtime-bug\runtime-bug.csproj]
obj\qsharp\src\Operations.g.cs(27,44): error CS1061: 'IQArray<long>' does not contain a 
definition for 'Item1' and no accessible extension method 'Item1' accepting a first argument of type 'IQArray<long>' could be found (are you missing a using directive or an assembly reference?) [C:\Users\<redacted>\tmp\runtime-bug\runtime-bug.csproj]        
obj\qsharp\src\Operations.g.cs(28,45): error CS1061: 'IQArray<long>' does not contain a 
definition for 'Item2' and no accessible extension method 'Item2' accepting a first argument of type 'IQArray<long>' could be found (are you missing a using directive or an assembly reference?) [C:\Users\<redacted>\tmp\runtime-bug\runtime-bug.csproj]        
obj\qsharp\src\Operations.g.cs(29,45): error CS1061: 'IQArray<long>' does not contain a 
definition for 'Item1' and no accessible extension method 'Item1' accepting a first argument of type 'IQArray<long>' could be found (are you missing a using directive or an assembly reference?) [C:\Users\<redacted>\tmp\runtime-bug\runtime-bug.csproj]        
obj\qsharp\src\Operations.g.cs(30,37): error CS1061: 'IQArray<long>' does not contain a 
definition for 'Item2' and no accessible extension method 'Item2' accepting a first argument of type 'IQArray<long>' could be found (are you missing a using directive or an assembly reference?) [C:\Users\<redacted>\tmp\runtime-bug\runtime-bug.csproj]        
obj\qsharp\src\Operations.g.cs(34,26): error CS1061: 'IQArray<long>' does not contain a 
definition for 'Item1' and no accessible extension method 'Item1' accepting a first argument of type 'IQArray<long>' could be found (are you missing a using directive or an assembly reference?) [C:\Users\<redacted>\tmp\runtime-bug\runtime-bug.csproj]        
obj\qsharp\src\Operations.g.cs(35,26): error CS1061: 'IQArray<long>' does not contain a 
definition for 'Item2' and no accessible extension method 'Item2' accepting a first argument of type 'IQArray<long>' could be found (are you missing a using directive or an assembly reference?) [C:\Users\<redacted>\tmp\runtime-bug\runtime-bug.csproj]  

In either case, when calling from IQ#, the kernel dies with no error message printed to the notebook or the console.

To Reproduce

open Microsoft.Quantum.Arrays;

newtype Foo = (Data: Int[]);

function Example() : Foo[] {
    return Mapped(Foo, [[1, 2], [3, 4, 5], new Int[0], [16]]);
}

function Boom() : Int {
    let foos = Example();
    return foos[0]::Data[0];
}

Renaming Data → NotData, the example works as expected.

See https://gist.github.com/cgranade/ee913899e0b40e8ee8cd43b82632a454 for IQ# version.

System information

• OS: Windows 10

• .NET Core Version: 3.0.100-preview8-013656

• IQ# Version: 0.8.1907.1701

Additional context
Add any other context about the problem here.

[bromeg]

This is a good opportunity to make sure everything generated in the C# code is a reserve pattern in Q#.

[anpaz]

Q# uses words starting with double underscore __ as reserved, so we should probably name Data like this (or make sure it doesn't collide by making sure Data is referenced to an interface.

[cgranade]

@anpaz-msft: For the approach of using an explicit interface implementation, it looks like modifying how QTuple<T> implements IQTuple<T>.Data would be the most logical, but that seems pretty heavyweight...