Add runtime property HOSTFXR_PATH

[mateoatr]

When executing the SDK CLI, set runtime property HOSTFXR_PATH with value equal to the loaded hostfxr path so that the SDK can locate it without having to rely on the heuristics of dlopen/LoadLibrary.

This property is only set when running the muxer and the application is dotnet.dll (that is, this property will only be set if we are about to execute a dotnet cli command).

[ghost]

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

Issue Details

---

When executing the SDK CLI, set runtime property HOSTFXR_PATH with value equal to the loaded hostfxr path so that the SDK can locate it without having to rely on the heuristics of dlopen/LoadLibrary.

This property is only set when running the muxer and the application is dotnet.dll (that is, this property will only be set if we are about to execute a dotnet cli command).

Author:	mateoatr
Assignees:	-
Labels:	area-Host
Milestone:	-

[elinor-fung]

Thoughts on adding a test for checking that HOSTFXR_PATH is set correctly? Maybe something like dummy SDK and mock coreclr, call dotnet such that it should run an SDK command, and check that the new property is logged out as expected.