[4680] Fix setting date separator handler not being applied

[MarinTolic]

🎯 Goal

Closes GetStream/android-internal-board#172

🛠 Implementation details

Implemented a method inside MessageListItemLiveData which updates the date separator handler.

🧪 Testing

Patch that logs separator handler calls

Index: stream-chat-android-ui-components-sample/src/main/kotlin/io/getstream/chat/ui/sample/feature/chat/ChatFragment.kt
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/stream-chat-android-ui-components-sample/src/main/kotlin/io/getstream/chat/ui/sample/feature/chat/ChatFragment.kt b/stream-chat-android-ui-components-sample/src/main/kotlin/io/getstream/chat/ui/sample/feature/chat/ChatFragment.kt
--- a/stream-chat-android-ui-components-sample/src/main/kotlin/io/getstream/chat/ui/sample/feature/chat/ChatFragment.kt	(revision b71509124a73e34ff5e0d869ea44a7ed2a1abd5d)
+++ b/stream-chat-android-ui-components-sample/src/main/kotlin/io/getstream/chat/ui/sample/feature/chat/ChatFragment.kt	(date 1676654206028)
@@ -17,6 +17,7 @@
 package io.getstream.chat.ui.sample.feature.chat
 
 import android.os.Bundle
+import android.util.Log
 import android.view.LayoutInflater
 import android.view.View
 import android.view.ViewGroup
@@ -223,6 +224,7 @@
             )
             bindView(binding.messageListView, viewLifecycleOwner)
             setDateSeparatorHandler { previousMessage, message ->
+                Log.d("dateSeparator", "called")
                 if (previousMessage == null) {
                     true
                 } else {
@@ -230,6 +232,7 @@
                 }
             }
             setThreadDateSeparatorHandler { previousMessage, message ->
+                Log.d("threadDateSeparator", "called")
                 if (previousMessage == null) {
                     false
                 } else {

1. Apply the patch above
2. Enter a channel and scroll
3. Enter a thread and scroll
4. Filter logs for dateSeparator and threadDateSeparator. You should see these being logged.
5. Go to v5 and apply the same patch
6. Repeat steps 2 and 3. You should not see dateSeparator being logged, threadDateSeparator will still be logged however

☑️Contributor Checklist

General

• Assigned a person / code owner group (required)
• Thread with the PR link started in a respective Slack channel (#android-chat-core or #android-chat-ui) (required)
• PR targets the develop branch
• PR is linked to the GitHub issue it resolves

Code & documentation

• Changelog is updated with client-facing changes
• New code is covered by unit tests
• Comparison screenshots added for visual changes
• Affected documentation updated (KDocs, docusaurus, tutorial)

☑️Reviewer Checklist

• UI Components sample runs & works
• Compose sample runs & works
• UI Changes correct (before & after images)
• Bugs validated (bugfixes)
• New feature tested and works
• Release notes and docs clearly describe changes
• All code we touched has new or updated KDocs

🎉 GIF