Infinite scroll added checks to validate input (#39618)

* Added isset checks to avoid Warnings

* changelog

* Added new isset for last_post_date

* Deprecate infinite_scroll_posts_where  hook

Committed via a GitHub action: https://github.com/Automattic/jetpack/actions/runs/11269962804

Upstream-Ref: Automattic/jetpack@8537542

jetpack_vendor/automattic/jetpack-sync/composer.json

@@ -16,7 +16,7 @@
 		"automattic/jetpack-changelogger": "^4.2.6",
 		"yoast/phpunit-polyfills": "^1.1.1",
 		"automattic/jetpack-search": "@dev",
-		"automattic/jetpack-waf": "@dev",
+		"automattic/jetpack-waf": "^0.22.0-alpha",
 		"automattic/wordbless": "@dev"
 	},
 	"suggest": {

vendor/composer/installed.json

@@ -1820,7 +1820,7 @@
             "dist": {
                 "type": "path",
                 "url": "/tmp/jetpack-build/Automattic/jetpack-sync",
-                "reference": "db234be1f7afe4a1f27c50c90c359e238f8583b5"
+                "reference": "3e966187609884caeb4dbf16982b133421142815"
             },
             "require": {
                 "automattic/jetpack-connection": "^5.1.3-alpha",
@@ -1834,7 +1834,7 @@
             "require-dev": {
                 "automattic/jetpack-changelogger": "^4.2.6",
                 "automattic/jetpack-search": "@dev",
-                "automattic/jetpack-waf": "@dev",
+                "automattic/jetpack-waf": "^0.22.0-alpha",
                 "automattic/wordbless": "@dev",
                 "yoast/phpunit-polyfills": "^1.1.1"
             },

vendor/composer/installed.php

@@ -265,7 +265,7 @@
         'automattic/jetpack-sync' => array(
             'pretty_version' => '3.14.0-alpha.1728373566',
             'version' => '3.14.0.0-alpha1728373566',
-            'reference' => 'db234be1f7afe4a1f27c50c90c359e238f8583b5',
+            'reference' => '3e966187609884caeb4dbf16982b133421142815',
             'type' => 'jetpack-library',
             'install_path' => __DIR__ . '/../../jetpack_vendor/automattic/jetpack-sync',
             'aliases' => array(),