cppgc: Enable pointer compression on Fuchsia

Pointer compression regresses binary size on Fuchsia by about 300K.
However, the change improves Oilpan memory by 15-20% (2-4% of PMF),
which is beneficial for memory-impoverished platforms.

Bug: chromium:1325007
Fuchsia-Binary-Size: See commit description.
Change-Id: Ie16fd992e45e29e264549a960e9755ec58da1691
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3829313Reviewed-by: Wez <wez@chromium.org>
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82572}

BUILD.gn

@@ -851,10 +851,12 @@ if (cppgc_enable_caged_heap) {
   cppgc_enable_young_generation = true
 
   if (is_linux || (is_mac && v8_current_cpu != "arm64") || is_win ||
-      is_chromeos || is_android) {
+      is_chromeos || is_android || is_fuchsia) {
     # Enable on all platforms but M1 and Fuchsia.
+    # Pointer compression regresses binary size on Fuchsia by about 300K.
+    # However, the change improves Oilpan memory by 15-20% (2-4% of PMF),
+    # which is beneficial for memory-impoverished platforms.
     # TODO(1325007): Fix MotionMark regressions on M1.
-    # TODO(1325007): Address binary size increase on Fuchsia.
     cppgc_enable_pointer_compression = true
   }
 }