prefs: Move some DebugOptions to Preferences and clean up (#34998)

- Move options configuring antialiasing and WebRender shader precache to
  the `Preferences` to group them with other related WebRender and DOM
  settings.
- Remove the option to disable antialiasing for canvases. This was
  unused.

Signed-off-by: Martin Robinson <mrobinson@igalia.com>

tests/wpt/meta/MANIFEST.json

@@ -503873,7 +503873,7 @@
         []
        ],
        "executorservo.py": [
-        "8b6db6091a84e9e83ec8d161fc86b1d0387f41e6",
+        "bc2021e1f5c05d55ce5a2a3fa35518efdd616415",
         []
        ],
        "executorservodriver.py": [

tests/wpt/tests/tools/wptrunner/wptrunner/executors/executorservo.py

@@ -231,7 +231,7 @@ class ServoRefTestExecutor(ServoExecutor):
             extra_args = ["--exit",
                           "--output=%s" % output_path,
                           "--window-size", viewport_size or "800x600"]
-            debug_opts = "disable-text-aa,replace-surrogates"
+            debug_opts = "replace-surrogates"
 
             if dpi:
                 extra_args += ["--device-pixel-ratio", dpi]