.NET: 'dotnet new tvos' creates a project that doesn't build

[rolfbjarne]

Steps to Reproduce

1. dotnet new tvos
2. Add a RuntimeIdentifier to the csproj (<RuntimeIdentifier>tvos-x64</RuntimeIdentifier>)
3. dotnet build

Expected Behavior

Build succeeds

Actual Behavior

Tool xcrun execution started with arguments: clang -g -mtvos-simulator-version-min=11.2 -arch x86_64 -isysroot /Applications/Xcode_13.0.0-beta.app/Contents/Developer/Platforms/AppleTVSimulator.platform/Developer/SDKs/AppleTVSimulator15.0.sdk -I/runtimes/tvos-x64/native -DDEBUG -o /Users/rolf/work/maccore/main/xamarin-macios/tests/dotnet/tvos/obj/Debug/net6.0-tvos/tvos-x64/nativelibraries/main.x86_64.o -c /Users/rolf/work/maccore/main/xamarin-macios/tests/dotnet/tvos/obj/Debug/net6.0-tvos/tvos-x64/linker-cache/main.x86_64.mm
         (TaskId:157)
Tool xcrun execution finished (exit code = 1).
         (TaskId:157)
/Users/rolf/work/maccore/main/xamarin-macios/tests/dotnet/tvos/obj/Debug/net6.0-tvos/tvos-x64/linker-cache/main.x86_64.mm:15:10: fatal error: 'xamarin/xamarin.h' file not found
#include "xamarin/xamarin.h"
         ^~~~~~~~~~~~~~~~~~~
1 error generated.
 (TaskId:157)

msbuild.binlog.zip

xamarin-macios: f9d0159

[rolfbjarne]

The reason is that this clang argument is wrong:

-I/runtimes/tvos-x64/native

part of the path is missing.

[akoeplinger]

tvos-x64 is not a valid RID, it should be tvossimulator-x64.

[rolfbjarne]

tvos-x64 is not a valid RID, it should be tvossimulator-x64.

Yeah, that works 🤦

We need RID validation sooner rather than later (which is a part of #10861)