Refactor actions to be entities with components (#19900)

Content.Shared/Mapping/StartPlacementActionEvent.cs

@@ -0,0 +1,18 @@
+using Content.Shared.Actions;
+
+namespace Content.Shared.Mapping;
+
+public sealed partial class StartPlacementActionEvent : InstantActionEvent
+{
+    [DataField("entityType")]
+    public string? EntityType;
+
+    [DataField("tileId")]
+    public string? TileId;
+
+    [DataField("placementOption")]
+    public string? PlacementOption;
+
+    [DataField("eraser")]
+    public bool Eraser;
+}