feat(plugin): add terrain3d plugin installation

addons/terrain_3d/menu/channel_packer_dragdrop.gd

@@ -0,0 +1,17 @@
+# Copyright © 2023-2026 Cory Petkovsek, Roope Palmroos, and Contributors.
+# Channel Packer Dragdropper for Terrain3D
+@tool
+extends Button
+
+signal dropped
+
+func _can_drop_data(p_position, p_data) -> bool:
+	if typeof(p_data) == TYPE_DICTIONARY:
+		if p_data.files.size() == 1:
+			match p_data.files[0].get_extension():
+				"png", "bmp", "exr", "hdr", "jpg", "jpeg", "tga", "svg", "webp", "ktx", "dds":
+					return true
+	return false
+
+func _drop_data(p_position, p_data) -> void:
+	dropped.emit(p_data.files[0])