Reduce knocked down players tile friction (#11035)

Content.Shared/Movement/Events/TileFrictionEvent.cs

@@ -0,0 +1,15 @@
+namespace Content.Shared.Movement.Events;
+
+/// <summary>
+/// Raised to try and get any tile friction modifiers for a particular body.
+/// </summary>
+[ByRefEvent]
+public struct TileFrictionEvent
+{
+    public float Modifier;
+
+    public TileFrictionEvent(float modifier)
+    {
+        Modifier = modifier;
+    }
+}