Implement InferType() for ldelema.

This improves decompilation of compound assignment on array elements.

ICSharpCode.Decompiler/CSharp/ExpressionBuilder.cs

@@ -1775,7 +1775,7 @@ namespace ICSharpCode.Decompiler.CSharp
 		{
 			TranslatedExpression arrayExpr = Translate(inst.Array);
 			var arrayType = arrayExpr.Type as ArrayType;
-			if (arrayType == null) {
+			if (arrayType == null || !TypeUtils.IsCompatibleTypeForMemoryAccess(new ByReferenceType(arrayType.ElementType), inst.Type)) {
 				arrayType  = new ArrayType(compilation, inst.Type, inst.Indices.Count);
 				arrayExpr = arrayExpr.ConvertTo(arrayType, this);
 			}

ICSharpCode.Decompiler/IL/ILTypeExtensions.cs

@@ -163,6 +163,14 @@ namespace ICSharpCode.Decompiler.IL
 					return new TypeSystem.ByReferenceType(ldflda.Field.Type);
 				case LdsFlda ldsflda:
 					return new TypeSystem.ByReferenceType(ldsflda.Field.Type);
+				case LdElema ldelema:
+					if (ldelema.Array.InferType() is TypeSystem.ArrayType arrayType) {
+						var refType = new TypeSystem.ByReferenceType(arrayType.ElementType);
+						if (TypeUtils.IsCompatibleTypeForMemoryAccess(refType, ldelema.Type)) {
+							return refType;
+						}
+					}
+					return new TypeSystem.ByReferenceType(ldelema.Type);
 				default:
 					return SpecialType.UnknownType;
 			}