[macos] Fix pdb mismatch when saving assemblies processed by mmp (#2901)

- https://bugzilla.xamarin.com/show_bug.cgi?id=60277
- Teach mmp and mtouch resolver to always ask for symbol reading from Cecil
- In most cases we explicitly load symbols (LoadReferencesStep) but when we don't rewritten assemblies don't match their pdb and we break debugging.

tools/mmp/resolver.cs

@@ -28,6 +28,7 @@
 using System.Security.Cryptography;
 
 using Mono.Cecil;
+using Mono.Cecil.Cil;
 
 namespace Xamarin.Bundler {
 	public partial class MonoMacResolver : IAssemblyResolver {
@@ -72,7 +73,9 @@ public AssemblyDefinition AddAssembly (string fileName)
 			assembly = AssemblyDefinition.ReadAssembly (fileName, new ReaderParameters 
 				{
 					AssemblyResolver = this,
-					InMemory = new FileInfo (fileName).Length < 1024 * 1024 * 100 // 100 MB
+					InMemory = new FileInfo (fileName).Length < 1024 * 1024 * 100, // 100 MB
+					ReadSymbols = true,
+					SymbolReaderProvider = new DefaultSymbolReaderProvider (throwIfNoSymbol: false) 
 				});
 			cache.Add (name, assembly);
 			return assembly;

tools/mtouch/AssemblyResolver.cs

@@ -16,6 +16,7 @@
 using System.Linq;
 
 using Mono.Cecil;
+using Mono.Cecil.Cil;
 using Mono.Tuner;
 
 using Xamarin.Bundler;
@@ -70,6 +71,8 @@ ReaderParameters CreateParameters (string path)
 			var parameters = new ReaderParameters ();
 			parameters.AssemblyResolver = this;
 			parameters.InMemory = new FileInfo (path).Length < 1024 * 1024 * 100; // 100 MB.
+			parameters.ReadSymbols = true;
+			parameters.SymbolReaderProvider = new DefaultSymbolReaderProvider (throwIfNoSymbol: false);
 			return parameters;
 		}