Finish treating the Unsafe APIs as JIT intrinsics

[tannergooding]

A majority of the APIs on System.Runtime.CompilerServices.Unsafe were converted to be JIT intrinsics as part of #68739 and later more as part of #85562

The remaining unhandled ones are:

• NI_SRCS_UNSAFE_CopyBlock
• NI_SRCS_UNSAFE_CopyBlockUnaligned
• NI_SRCS_UNSAFE_InitBlock
• NI_SRCS_UNSAFE_InitBlockUnaligned
• NI_SRCS_UNSAFE_Unbox

We should ensure these are likewise handled as JIT intrinsics to further improve code quality and JIT throughput where possible

category:implementation
theme:intrinsics
skill-level:intermediate
cost:small
impact:small

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Issue Details

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A majority of the APIs on System.Runtime.CompilerServices.Unsafe were converted to be JIT intrinsics as part of #68739.

The remaining unhandled ones are:

• NI_SRCS_UNSAFE_Copy
• NI_SRCS_UNSAFE_CopyBlock
• NI_SRCS_UNSAFE_CopyBlockUnaligned
• NI_SRCS_UNSAFE_InitBlock
• NI_SRCS_UNSAFE_InitBlockUnaligned
• NI_SRCS_UNSAFE_Read
• NI_SRCS_UNSAFE_ReadUnaligned
• NI_SRCS_UNSAFE_Unbox
• NI_SRCS_UNSAFE_Write
• NI_SRCS_UNSAFE_WriteUnaligned

We should ensure these are likewise handled as JIT intrinsics to further improve code quality and JIT throughput where possible

Author:	tannergooding
Assignees:	-
Labels:	area-CodeGen-coreclr
Milestone:	-

[jkotas]

Once this is done, we can switch these intrinsics onto the same plan as hardware intrinsics, implement them using self-recursive pattern in C# and delete the IL intrinsic expansion in VM/AOT (getILIntrinsicImplementationForUnsafe and Internal.IL.Stubs.UnsafeIntrinsics).

[JulieLeeMSFT]

Cc @dotnet/jit-contrib.

[deeprobin]

Is this easy for JIT-newbies?

[MichalPetryka]

NI_SRCS_UNSAFE_Copy, NI_SRCS_UNSAFE_Read, NI_SRCS_UNSAFE_ReadUnaligned, NI_SRCS_UNSAFE_Write and NI_SRCS_UNSAFE_WriteUnaligned can be removed from the list now.