Reland "cppgc: Enable pointer compression by default on Desktop"

Now that the marking verifier doesn't verify stack, reenable PC.

Bug: chromium:1325007
Change-Id: I85c4ed0a76cf84992781966d3694211e8ea36a1d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3785147
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82001}

BUILD.gn

@@ -834,6 +834,12 @@ if (cppgc_enable_caged_heap) {
 
   # Always enable young generation compile time flag if caged heap is enabled.
   cppgc_enable_young_generation = true
+
+  if (is_linux || is_mac || is_win) {
+    # Always enable on desktop but avoid on ChromeOS for now (for stability
+    # reasons).
+    cppgc_enable_pointer_compression = true
+  }
 }
 if (cppgc_enable_young_generation) {
   enabled_external_cppgc_defines += [ "CPPGC_YOUNG_GENERATION" ]