[netcore] Enable ALC loaded_assemblies (mono/mono#15850)

[netcore] Enable ALC loaded_assemblies (mono/mono#15850)

* Typo

* Enable loaded_assemblies and lock

* Make mono_domain_assembly_open_internal ALC-aware

* Populate loaded_assemblies

Switch from prepend to append

* Some notes

* Exclude add_assembly_to_alc on non-netcore

* Cleanup appdomain.c

* Remove mono_alc_cleanup for now

* Update comment

* Disable using loaded_assemblies in the search hook

* Adjust alc cleanup

Commit migrated from https://github.com/mono/mono/commit/848811e4b26519ce62672886813f6eb73d572be5