[appdomain] Use coop handles for most methods in System.AppDomain (#4286)

[appdomain] Use coop handles for most methods in System.AppDomain (#4286)

* [runtime] Use coop handles for ves_icall_System_AppDomain_GetData

* [runtime] Add mono_string_new_utf16_handle function that returns a MonoStringHandle

* [runtime] Use coop handles for ves_icall_System_AppDomain_InternalGetProcessGuid

* [runtime] Use coop handles for System.AppDomain icalls

  - ves_icall_System_AppDomain_InternalIsFinalizingForUnload
  - ves_icall_System_AppDomain_InternalPushDomainRef
  - ves_icall_System_AppDomain_InternalPushDomainRefByID
    (This one is slightly non-trivial because we switch from MonoException to MonoError)
  - ves_icall_System_AppDomain_InternalPopDomainRef
  - ves_icall_System_AppDomain_InternalSetDomainByID

* [runtime] Use coop handles for ves_icall_System_AppDomain_InternalSetDomain

* [runtime] Use coop handles for ves_icall_System_AppDomain_SetData

* [runtime] Coop handles for some AppDomain icalls

  - ves_icall_System_AppDomain_getCurDomain
  - ves_icall_System_AppDomain_getFriendlyName
  - ves_icall_System_AppDomain_getRootDomain
  - ves_icall_System_AppDomain_getSetup

* [coop handles] Add mono_string_handle_length function

* [marshal] Add mono_marshal_xdomain_copy_value_handle

* [coop handles] Add mono_aray_new_full_handle

* [appdomain] Use handles in mono_array_clone_in_domain

* [runtime] Use coop handles for ves_icall_System_AppDomain_createDomain

* [appdomain] Use coop handles for ves_icall_System_AppDomain_InternalUnload