add agg result proxy

force-app/main/default/classes/proxies/AggregateResultProxy.cls

@@ -0,0 +1,31 @@
+public with sharing class AggregateResultProxy {
+  private Map<String, Object> valuesByAlias = new Map<String, Object>();
+
+  private AggregateResultProxy() {
+  }
+
+  public static AggregateResultProxy fromAggregateResult(AggregateResult item) {
+    String itemJson = JSON.serialize(item);
+    AggregateResultProxy proxy = new AggregateResultProxy();
+    proxy.valuesByAlias = (Map<String, Object>) JSON.deserializeUntyped(
+      itemJson
+    );
+    return proxy;
+  }
+
+  public static AggregateResultProxy fromMap(Map<String, Object> pairs) {
+    AggregateResultProxy proxy = new AggregateResultProxy();
+    proxy.valuesByAlias = new Map<String, Object>(pairs);
+    return proxy;
+  }
+
+  public static AggregateResultProxy fromPair(String key, Object value) {
+    AggregateResultProxy proxy = new AggregateResultProxy();
+    proxy.valuesByAlias = new Map<String, Object>{ key => value };
+    return proxy;
+  }
+
+  public Map<String, Object> getValuesByAlias() {
+    return this.valuesByAlias;
+  }
+}

force-app/main/default/classes/proxies/AggregateResultProxy.cls-meta.xml

@@ -0,0 +1,5 @@
+<?xml version="1.0" encoding="UTF-8" ?>
+<ApexClass xmlns="http://soap.sforce.com/2006/04/metadata">
+    <apiVersion>61.0</apiVersion>
+    <status>Active</status>
+</ApexClass>