Refactor relief rendering and generation logic

- Migrate relief icon rendering from SVG to WebGL for improved performance.
- Introduce a new relief generator module to handle relief icon creation.
- Update event listeners in relief editor to use a consistent `byId` method.
- Synchronize relief data with the current SVG DOM when exiting edit mode.
- Enhance relief icon management by integrating new utility functions for generating and resolving relief icons.
- Clean up legacy code and improve overall structure for better maintainability.

public/modules/ui/style.js

@@ -729,19 +729,22 @@ styleHeightmapCurve.on("change", e => {
 
 styleReliefSet.on("change", e => {
   terrain.attr("set", e.target.value);
-  drawReliefIcons();
+  pack.relief = [];
+  drawRelief();
   if (!layerIsOn("toggleRelief")) toggleRelief();
 });
 
 styleReliefSize.on("change", e => {
   terrain.attr("size", e.target.value);
-  drawReliefIcons();
+  pack.relief = [];
+  drawRelief();
   if (!layerIsOn("toggleRelief")) toggleRelief();
 });
 
 styleReliefDensity.on("change", e => {
   terrain.attr("density", e.target.value);
-  drawReliefIcons();
+  pack.relief = [];
+  drawRelief();
   if (!layerIsOn("toggleRelief")) toggleRelief();
 });