Use more spans in System.Reflection.Metadata et. al.

[teo-tsirpanis]

This PR among other things changes the buffer code of System.Reflection.Metadata so that it uses spans and framework methods that are more optimized, and reduces pinning and unsafely converting between immutable and mutable arrays.

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Issue Details

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This PR among other things changes the buffer code of System.Reflection.Metadata so that it uses spans and framework methods that are more optimized, and reduces pinning and unsafely converting between immutable and mutable arrays.

Author:	teo-tsirpanis
Assignees:	-
Labels:	area-System.Reflection.Metadata
Milestone:	-

[stephentoub]

Nit: You could tidy this (and the others like it) up to just be:

public static void WriteUInt16(this byte[] buffer, int start, ushort value) =>
    Unsafe.WriteUnaligned(ref buffer[start], BitConverter.IsLittleEndian ? BinaryPrimitives.ReverseEndianness(value) : value);

[teo-tsirpanis]

Done.

[steveharter]

Are there any remaining CI issues? There were some Mono build failures, but I suspect infrastructure and just re-ran those.

[steveharter]

@teo-tsirpanis can you rebase to the latest? There are these build errors that have already recently been fixed (see this PR):

D:\a\_work\1\s\src\mono\dlls\mscordbi\cordb-value.cpp(351): error C2259: 'CordbArrayValue': cannot instantiate abstract class
2022-10-26T18:05:27.8469947Z   D:\a\_work\1\s\src\mono\dlls\mscordbi\cordb-value.h(170): note: see declaration of 'CordbArrayValue'
2022-10-26T18:05:27.8905158Z   D:\a\_work\1\s\src\mono\dlls\mscordbi\cordb-value.cpp(351): note: due to following members:

[teo-tsirpanis]

Done @steveharter.

[stephentoub]

Thanks.