[build] Create clr.host subset to remove patching step for mono runtime tests

[naricc]

This pr creates a clr.hosts subset that allows corerun to be built independently from coreclr. It also copies the mono version of libcoreclr to the core_root directory during the runtime test build, so that corerun will use it when running the tests.

This simplifies the process of running the runtime tests against mono, by removing the requirement to build coreclr first and the patch it with mono libraries. This should make it easier to reproduce the test runs locally, and also remove a potential source of erros in CI.

There will be follow up PRs to enable CI to actually use this.

I am sure I must have missed some necessary checks somewhere, but this seems to work locally.

This partially addresses #43952 but I will need to do the CI component before that is complete.

Contributes to #58266

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Issue Details

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This pr creates a clr.hosts subset that allows corerun to be built independently from coreclr. It also copies the mono version of libcoreclr to the core_root directory during the runtime test build, so that corerun will use it when running the tests.

This simplifies the process of running the runtime tests against mono, by removing the requirement to build coreclr first and the patch it with mono libraries. This should make it easier to reproduce the test runs locally, and also remove a potential source of erros in CI.

There will be follow up PRs to enable CI to actually use this.

I am sure I must have missed some necessary checks somewhere, but this seems to work locally.

This partially addresses #43952 but I will need to do the CI component before that is complete.

Author:	naricc
Assignees:	-
Labels:	area-Infrastructure
Milestone:	-

[trylek]

LGTM, thank you!

[lambdageek]

A few nits:

1. use the TargetsXYZ props consistently
2. we missed tvOS
3. style nit:'$(Cond)' == 'true' like elsewhere