Move startup hook tests targeting `StartupHookProvider` out of hosting tests

[elinor-fung]

Many StartupHook tests (and test projects) are actually targeting StartupHookProvider, not the hosting side of it. They can be moved to coreclr and just call into StartupHookProvider without launching a bunch of processes to actually run an app.

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

Tagging subscribers to this area: @vitek-karas, @agocke, @VSadov
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Many StartupHook tests (and test projects) are actually targeting StartupHookProvider, not the hosting side of it. They can be moved to coreclr and just call into StartupHookProvider without launching a bunch of processes to actually run an app.

Author:	elinor-fung
Assignees:	-
Labels:	test-enhancement, area-Host, untriaged
Milestone:	-