Web: Disable raycast module by default (no occlusion culling)

This means no CPU occlusion culling (and not compiling Embree), unless
you compile custom export templates with `module_raycast_enabled=yes`.

This reduces the memory footprint significantly, and binary size.

Fixes #70621.

Co-authored-by: Hugo Locurcio <hugo.locurcio@hugo.pro>
(cherry picked from commit 8c40edf8c0)

platform/web/detect.py

@@ -60,6 +60,8 @@ def get_flags():
         ("target", "template_debug"),
         ("builtin_pcre2_with_jit", False),
         ("vulkan", False),
+        # Embree is heavy and requires too much memory (GH-70621).
+        ("module_raycast_enabled", False),
         # Use -Os to prioritize optimizing for reduced file size. This is
         # particularly valuable for the web platform because it directly
         # decreases download time.