Reland "[roheap] Enable shared ro-heap by default if ptr compression is disabled"

This is a reland of fb4d5480

Few test-serialize tests were not clearing the shared heap before using a
new snapshot, breaking the noembed build. This is fixed now and a check
has been added
(https://chromium-review.googlesource.com/c/v8/v8/+/1667415) to make
sure it doesn't happen again.

Original change's description:
> [roheap] Enable shared ro-heap by default if ptr compression is disabled
>
> Shared read-only heap is currently incompatible with pointer compression.
> Enable sharing only if pointer compression is disabled.
>
> Bug: v8:7464
> Change-Id: I0866ac288a34eb92fc227e8beba57f4d72a69ef0
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1635509
> Reviewed-by: Dan Elphick <delphick@chromium.org>
> Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
> Commit-Queue: Maciej Goszczycki <goszczycki@google.com>
> Cr-Commit-Position: refs/heads/master@{#61963}

Bug: v8:7464
Change-Id: Ie7d09cebf897a3f0e4a6c103ad0c132c4faf6c6e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1667418Reviewed-by: Dan Elphick <delphick@chromium.org>
Commit-Queue: Maciej Goszczycki <goszczycki@google.com>
Cr-Commit-Position: refs/heads/master@{#62425}

BUILD.gn

@@ -228,7 +228,7 @@ if (v8_enable_snapshot_native_code_counters == "") {
   v8_enable_snapshot_native_code_counters = v8_enable_debugging_features
 }
 if (v8_enable_shared_ro_heap == "") {
-  v8_enable_shared_ro_heap = v8_enable_lite_mode
+  v8_enable_shared_ro_heap = !v8_enable_pointer_compression && v8_use_snapshot
 }
 if (v8_enable_fast_torque == "") {
   v8_enable_fast_torque = v8_enable_fast_mksnapshot