Please clarify if System.Tuple counts as a tuple type.

The documentation is somewhat unclear on when a symbol is considered to be a tuple, as there are two kinds of tuples in the standard library. Does it only count for `System.ValueTuple` because of its special metadata, or does it include `System.Tuple` too?

It would be nice to rewrite the summary to clarify this, since there already exists a typo as well:

> "Is this a symbol for a tuple ."

I would make a PR, however I would rather have someone else write it who knows what goes on under the hood.

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* ID: 89140689-8c0c-0709-10f7-c793eef2c094
* Version Independent ID: 1fb23a39-66df-af9f-1816-8ffb4f66e90c
* Content: [ITypeSymbol.IsTupleType Property (Microsoft.CodeAnalysis)](https://learn.microsoft.com/en-us/dotnet/api/microsoft.codeanalysis.itypesymbol.istupletype?view=roslyn-dotnet-4.6.0&viewFallbackFrom=netstandard-2.0)
* Content Source: [dotnet/xml/Microsoft.CodeAnalysis/ITypeSymbol.xml](https://github.com/dotnet/roslyn-api-docs/blob/live/dotnet/xml/Microsoft.CodeAnalysis/ITypeSymbol.xml)
* Product: **dotnet-roslyn-api**
* Technology: **microsoft.codeanalysis**
* GitHub Login: @dotnet-bot
* Microsoft Alias: **dotnetcontent**