Update the CHANGELOG.md for a 85.3 release (flutter#8127)

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Author: jwren

CHANGELOG.md

@@ -1,3 +1,8 @@
+# 85.3
+- Add Property Editor side panel (#7957)
+- Support removed for IDEA 2024.1 (Koala) and 2024.2 (Ladybug) (#8073)
+- Various cleanups including migrating slow operations to non-blocking calls (#8089)
+
 # 85.2
 - Fix broken devtools inspector source navigation (#8041)
 

resources/META-INF/plugin.xml

@@ -50,6 +50,12 @@
 
   <change-notes>
     <![CDATA[
+<h1>85.3</h1>
+<ul>
+  <li>Add Property Editor side panel (#7957)</li>
+  <li>Support removed for IDEA 2024.1 (Koala) and 2024.2 (Ladybug) (#8073)</li>
+  <li>Various cleanups including migrating slow operations to non-blocking calls (#8089)</li>
+</ul>
 <h1>85.2</h1>
 <ul>
   <li>Fix broken devtools inspector source navigation (#8041)</li>