[release/9.0.1xx] [ObjCRuntime] Ensure all assemblies' module constructors have executed before failing registrar lookup. (#21891)

The managed static registrar depends on each assembly registering itself
to
find types from that assembly. This is done using a module constructor,
but
the module constructor isn't necessarily executed before the managed
static
registrar needs the assembly registered (in particular for app
extensions,
which don't have a managed entry point).

That would lead to exceptions like this:

*** Terminating app due to uncaught exception
'ObjCRuntime.RuntimeException', reason: 'Could not find the type
'ObjCRuntime.__Registrar__' in the assembly '...'.
(ObjCRuntime.RuntimeException)
		at ObjCRuntime.RegistrarHelper.GetMapEntry(String assemblyName)
		at ObjCRuntime.RegistrarHelper.GetMapEntry(Assembly assembly)
		[...]

Fix this by manually calling the module constructor for every loaded
assembly
if we can't find it in the map of registered assemblies.


Backport of #21885

Co-authored-by: Rolf Bjarne Kvinge <rolf@xamarin.com>

Author: vs-mobiletools-engineering-service2

src/ObjCRuntime/RegistrarHelper.cs

@@ -102,6 +102,25 @@ static MapInfo GetMapEntry (string assemblyName)
 		{
 			if (TryGetMapEntry (assemblyName, out var rv))
 				return rv;
+
+#if TRACE
+			Runtime.NSLog ($"RegistrarHelper.GetMapEntry ({assemblyName}) => failed to find entry, will ensure module constructors are called for all loaded assemblies.");
+#endif
+			// An assembly is only registered if we've (tried to) execute code from it, which is not guaranteed to
+			// happen before we get here (in particular for app extensions, which don't have a managed Main method).
+			// So here we loop over all the assemblies in the current domain, make sure the module constructor
+			// has been called for all of them, and then we try again.
+			var assemblies = AppDomain.CurrentDomain.GetAssemblies ();
+			foreach (var asm in assemblies)
+				RuntimeHelpers.RunModuleConstructor (asm.ManifestModule.ModuleHandle);
+
+			if (TryGetMapEntry (assemblyName, out rv))
+				return rv;
+
+#if TRACE
+			Runtime.NSLog ($"RegistrarHelper.GetMapEntry ({assemblyName}) => failed to find entry for the second time.");
+#endif
+
 			throw ErrorHelper.CreateError (8055, Errors.MX8055 /* Could not find the type 'ObjCRuntime.__Registrar__' in the assembly '{0}' */, assemblyName);
 		}