Create .NET (Core) version of Reflection doc

I only see this one, which includes CodeDom, which we don't want.

https://docs.microsoft.com/en-us/dotnet/framework/reflection-and-codedom/reflection

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#### Document Details

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* ID: 6179c09e-4a12-e0bc-a599-bbddad5bbc99
* Version Independent ID: d4baad38-e5e4-e247-9465-ed125804dc16
* Content: [Reflection in .NET - .NET Framework](https://docs.microsoft.com/en-us/dotnet/framework/reflection-and-codedom/reflection)
* Content Source: [docs/framework/reflection-and-codedom/reflection.md](https://github.com/dotnet/docs/blob/main/docs/framework/reflection-and-codedom/reflection.md)
* Product: **dotnet-framework**
* GitHub Login: @adegeo
* Microsoft Alias: **adegeo**