Start sharing code between ILLink/ILCompiler test infra

[sbomer]

This creates a new directory Mono.Linker.Tests.Shared with sources that are shared between the test infra of ILLink/ILCompiler. This starts by sharing most of the code in TestRunner.cs, renaming some types to make the sharing easier.

[ghost]

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Issue Details

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This creates a new directory Mono.Linker.Tests.Shared with sources that are shared between the test infra of ILLink/ILCompiler. This starts by sharing most of the code in TestRunner.cs, renaming some types to make the sharing easier.

Author:	sbomer
Assignees:	sbomer
Labels:	area-Tools-ILLink
Milestone:	-

[agocke]

LGTM, minor comments

[sbomer]

@mrvoorhe PTAL. This is renaming some of the types used in the test infra, so I wanted to run this approach by you.

[mrvoorhe]

Thanks. This looks okay.

[sbomer]

Failures are #81911 and #91344.

[vitek-karas]

Sorry for the late response. Only naming comments - suggestions.

[sbomer]

@vitek-karas I addressed your feedback in #91358. I went with Trimming since that's what I had been using for the shared type names. So ILCompiler.Trimming.Tests, Trimming.Tests.Shared, CustomizeTrimming, etc.