Add C# multi-dimension array versions of the Benchstones tests

[BruceForstall]

The Benchstones tests using multi-dimension arrays currently are
implemented using C# "jagged" arrays. Add versions of the tests
that use true C# multi-dimensional arrays. The code is exactly
the same, except for the array creation and indexing.

This will allow us to compare code generated for each, as well as
to verify functionality. I intend to add versions of these to the
microbenchmarks in the https://github.com/dotnet/performance repo as well.

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Issue Details

---

The Benchstones tests using multi-dimension arrays currently are
implemented using C# "jagged" arrays. Add versions of the tests
that use true C# multi-dimensional arrays. The code is exactly
the same, except for the array creation and indexing.

This will allow us to compare code generated for each, as well as
to verify functionality. I intend to add versions of these to the
microbenchmarks in the https://github.com/dotnet/performance repo as well.

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

[BruceForstall]

/azp run runtime-coreclr outerloop

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[BruceForstall]

@dotnet/jit-contrib PTAL

[BruceForstall]

/azp run runtime-coreclr outerloop

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[BruceForstall]

Failures are Assert failure(PID 3364 [0x00000d24], Thread: 5828 [0x16c4]): m_pLayoutLock->IsWriterLock() -- already fixed.