Warn on instrumenting unsupported types for the Fuzzer

[MihaZupan]

No description provided.

[buyaa-n]

NIT: maybe add in the doc something like If the type is in 'System' namespace use full type name instead of 'System' namespace., we can update it later

runtime/src/libraries/Fuzzing/DotnetFuzzing/IFuzzer.cs

Lines 15 to 17 in 4d37f40

	/// <summary>List of prefixes (CoreLib namespaces/types) that should be instrumented.
	/// If the code under test is outside CoreLib, you may return an empty array.</summary>
	string[] TargetCoreLibPrefixes { get; }

[buyaa-n]

Thanks!

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