Implement deep CustomDebugInformations copy

Previously, `AsyncMethodBodyDebugInformation` and
`StateMachineScopeDebugInformation` instances of cloned
method bodys would still refer to the old method bodies, which could
cause the PDB instruction offsets to desync. This change fixes this by
explicitly cloning them along with the method body.

Author: Popax21

Utils/Extensions.Relinker.cs

@@ -120,9 +120,33 @@ public static MethodBody Clone(this MethodBody bo, MethodDefinition m) {
             }));
 
 #if !CECIL0_9
-            m.CustomDebugInformations.AddRange(bo.Method.CustomDebugInformations); // Abstract. TODO: Implement deep CustomDebugInformations copy.
+            Instruction ResolveInstrOff(int off) {
+                // Can't check cloned instruction offsets directly, as those can change for some reason
+                for (int i = 0; i < bo.Instructions.Count; i++)
+                    if (bo.Instructions[i].Offset == off)
+                        return bc.Instructions[i];
+                throw new ArgumentException($"Invalid instruction offset {off}");
+            }
+
+            m.CustomDebugInformations.AddRange(bo.Method.CustomDebugInformations.Select(o => {
+                if (o is AsyncMethodBodyDebugInformation ao) {
+                    AsyncMethodBodyDebugInformation c = new AsyncMethodBodyDebugInformation();
+                    if (ao.CatchHandler.Offset >= 0)
+                        c.CatchHandler = ao.CatchHandler.IsEndOfMethod ? new InstructionOffset() : new InstructionOffset(ResolveInstrOff(ao.CatchHandler.Offset));
+                    c.Yields.AddRange(ao.Yields.Select(off => off.IsEndOfMethod ? new InstructionOffset() : new InstructionOffset(ResolveInstrOff(off.Offset))));
+                    c.Resumes.AddRange(ao.Resumes.Select(off => off.IsEndOfMethod ? new InstructionOffset() : new InstructionOffset(ResolveInstrOff(off.Offset))));
+                    c.ResumeMethods.AddRange(ao.ResumeMethods);
+                    return c;
+                } else if (o is StateMachineScopeDebugInformation so) {
+                    StateMachineScopeDebugInformation c = new StateMachineScopeDebugInformation();
+                    c.Scopes.AddRange(so.Scopes.Select(s => new StateMachineScope(ResolveInstrOff(s.Start.Offset), s.End.IsEndOfMethod ? null : ResolveInstrOff(s.End.Offset))));
+                    return c;
+                } else
+                    return o;
+            }));
+
             m.DebugInformation.SequencePoints.AddRange(bo.Method.DebugInformation.SequencePoints.Select(o => {
-                SequencePoint c = new SequencePoint(bc.Instructions.FirstOrDefault(i => i.Offset == o.Offset), o.Document);
+                SequencePoint c = new SequencePoint(ResolveInstrOff(o.Offset), o.Document);
                 c.StartLine = o.StartLine;
                 c.StartColumn = o.StartColumn;
                 c.EndLine = o.EndLine;