Added chat window transparency slider to options (#24990)

* Adds a new slider to the misc tab in options that lets the player set chat window transparency

* Tweaked variable names

* Fixed order to match UI

* Renamed set chat window transparency function

* Changed and refactored to opacity instead of transparency

* Remove unnecessary int to float conversions

Slider used to be 0-100 while the CCVar was 0.0-1.0f. This is confusing and was only used for rounding to 2 decimal points.

* Round the value to two decimal points

* Remove rounding for now

* Rename

* Unhardcode chat color by moving to stylesheet

* Fix indent

* Make opacity slider only change opacity

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Co-authored-by: Your Name <you@example.com>
Co-authored-by: ShadowCommander <10494922+ShadowCommander@users.noreply.github.com>

Content.Client/UserInterface/Systems/Chat/Controls/ChatInputBox.xaml.cs

@@ -1,4 +1,5 @@
-using Content.Shared.Chat;
+using Content.Client.Stylesheets;
+using Content.Shared.Chat;
 using Content.Shared.Input;
 using Robust.Client.UserInterface.Controls;
 
@@ -44,6 +45,7 @@ public class ChatInputBox : PanelContainer
             StyleClasses = {"chatFilterOptionButton"}
         };
         Container.AddChild(FilterButton);
+        AddStyleClass(StyleNano.StyleClassChatSubPanel);
         ChannelSelector.OnChannelSelect += UpdateActiveChannel;
     }