Change Enum.GetValues to AOT compatible call

[conniey]

Our team wants to use this package to parse KQL but a requirement is that packages must be AOT compatible. Currently, we get the warning when trying to publish AOT. This fixes that warning.

    D:\git\microsoft\Kusto-Query-Language\src\Kusto.Language\Syntax\SyntaxFacts.cs(775,25): 
    warning IL3050: Using member 'System.Enum.GetValues(Type)' which has 'RequiresDynamicCodeAttribute' can break functionality when AOT compiling. 
    It might not be possible to create an array of the enum type at runtime. 
    Use the GetValues<TEnum> overload or the GetValuesAsUnderlyingType method instead.

[mattwar]

We can't actually merge pull requests directly into this repo, as it is only a mirror of an internal Microsoft repo. However, I will make this fix for you.

[conniey]

@mattwar thank you!