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

Reland since ubsan failures were fixed.

Original change's description:
> Revert "cppgc: Enable pointer compression by default on Desktop"
>
> This reverts commit 4cf08c1a.
>
> Reason for revert: broke ubsan.
>
> Original change's description:
> > cppgc: Enable pointer compression by default on Desktop
> >
> > The CL enables pointer compression in Oilpan.
> >
> > For sherrifs: the CL may cause some slight perf regressions (likely
> > blink_perf.*), due to slightly higher cost of compression and
> > decomrpession.
> >
> > Speedometer2 is not expected to regress, as was checked locally. Such a
> > slight performance degradation is compensated by memory savings that are
> > expected to be around 10-20% of Oilpan committed size (~2.5-5% of Renderer
> > PMF).
> >
> > Bug: chromium:1325007
> > Change-Id: I2e31fc56250dbe6354a7614fa1f9e926260d842b
> > Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3695565
> > Commit-Queue: Anton Bikineev <bikineev@chromium.org>
> > Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
> > Cr-Commit-Position: refs/heads/main@{#81442}
>
> Bug: chromium:1325007
> Change-Id: Iabc31ed683841ba0189dee9028da330dc03d7e09
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3735168
> Auto-Submit: Anton Bikineev <bikineev@chromium.org>
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Commit-Queue: Anton Bikineev <bikineev@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#81443}

Bug: chromium:1325007
Change-Id: Ifc8ea0e73e99d9be622e27d3d4c79d0e35fd459c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3735128
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#81486}

BUILD.gn

@@ -812,6 +812,12 @@ 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" ]