Check that autoconsentMessageCallback exists before calling it (#7687)

Task/Issue URL:
https://app.asana.com/1/137249556945/task/1213142040936086

### Description

- Adds a guard around the JS in `ReplyHandler` to check that the
function exists before calling it.

### Steps to test this PR

- [ ] Smoke test autoconsent


<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> **Low Risk**
> Small, localized change to injected JS string construction plus test
updates; behavior only differs when the callback is absent (now no-op
instead of error).
> 
> **Overview**
> Prevents JavaScript reply injection from throwing when
`window.autoconsentMessageCallback` is missing by wrapping callback
invocation in a `typeof ... === 'function'` guard in
`ReplyHandler.constructReply`.
> 
> Updates affected tests to expect the new multi-line guarded JS and
loosens JSON extraction in handler plugin tests by parsing the substring
between `window.autoconsentMessageCallback(` and `, window.origin`
instead of relying on an exact wrapper prefix/suffix.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
903c125. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Author: joshliebe

autoconsent/autoconsent-impl/src/main/java/com/duckduckgo/autoconsent/impl/handlers/ReplyHandler.kt

@@ -18,6 +18,12 @@ package com.duckduckgo.autoconsent.impl.handlers
 
 object ReplyHandler {
     fun constructReply(message: String): String {
-        return "(function() {window.autoconsentMessageCallback($message, window.origin);})();"
+        return """
+            (function() {
+                if (typeof window.autoconsentMessageCallback === 'function') {
+                    window.autoconsentMessageCallback($message, window.origin);
+                }
+            })();
+        """.trimIndent()
     }
 }

autoconsent/autoconsent-impl/src/test/java/com/duckduckgo/autoconsent/impl/RealAutoconsentTest.kt

@@ -129,7 +129,13 @@ class RealAutoconsentTest {
 
     @Test
     fun whenSetAutoconsentOptOutThenEvaluateJavascriptCalled() {
-        val expected = """javascript:(function() {window.autoconsentMessageCallback({ "type": "optOut" }, window.origin);})();"""
+        val expected = """
+            javascript:(function() {
+                if (typeof window.autoconsentMessageCallback === 'function') {
+                    window.autoconsentMessageCallback({ "type": "optOut" }, window.origin);
+                }
+            })();
+        """.trimIndent()
 
         autoconsent.setAutoconsentOptOut(webView)
         assertEquals(expected, shadowOf(webView).lastEvaluatedJavascript)

autoconsent/autoconsent-impl/src/test/java/com/duckduckgo/autoconsent/impl/handlers/EvalMessageHandlerPluginTest.kt

@@ -117,9 +117,8 @@ class EvalMessageHandlerPluginTest {
     }
 
     private fun jsonToEvalResp(json: String): EvalResp? {
-        val trimmedJson = json
-            .removePrefix("javascript:(function() {window.autoconsentMessageCallback(")
-            .removeSuffix(", window.origin);})();")
+        val afterPrefix = json.substringAfter("window.autoconsentMessageCallback(")
+        val trimmedJson = afterPrefix.substringBefore(", window.origin")
         val moshi = Moshi.Builder().add(JSONObjectAdapter()).build()
         val jsonAdapter: JsonAdapter<EvalResp> = moshi.adapter(EvalResp::class.java)
         return jsonAdapter.fromJson(trimmedJson)

autoconsent/autoconsent-impl/src/test/java/com/duckduckgo/autoconsent/impl/handlers/InitMessageHandlerPluginTest.kt

@@ -369,9 +369,8 @@ class InitMessageHandlerPluginTest {
     }
 
     private fun jsonToInitResp(json: String): InitResp? {
-        val trimmedJson = json
-            .removePrefix("javascript:(function() {window.autoconsentMessageCallback(")
-            .removeSuffix(", window.origin);})();")
+        val afterPrefix = json.substringAfter("window.autoconsentMessageCallback(")
+        val trimmedJson = afterPrefix.substringBefore(", window.origin")
         val moshi = Moshi.Builder().add(JSONObjectAdapter()).build()
         val jsonAdapter: JsonAdapter<InitResp> = moshi.adapter(InitResp::class.java)
         return jsonAdapter.fromJson(trimmedJson)

autoconsent/autoconsent-impl/src/test/java/com/duckduckgo/autoconsent/impl/handlers/OptOutAndAutoconsentDoneMessageHandlerPluginTest.kt

@@ -95,7 +95,13 @@ class OptOutAndAutoconsentDoneMessageHandlerPluginTest {
 
     @Test
     fun whenProcessOptOutWithSelfTestThenAutoconsentCallsEvaluateJavascript() {
-        val expected = """javascript:(function() {window.autoconsentMessageCallback({ "type": "selfTest" }, window.origin);})();"""
+        val expected = """
+            javascript:(function() {
+                if (typeof window.autoconsentMessageCallback === 'function') {
+                    window.autoconsentMessageCallback({ "type": "selfTest" }, window.origin);
+                }
+            })();
+        """.trimIndent()
 
         handler.process(getOptOut(), optOutMessage(result = true, selfTest = true), webView, mockCallback)
         handler.process(getAutoconsentType(), autoconsentDoneMessage(), webView, mockCallback)