[ptr-cage] Disable shared pointer cage by default.

Bug: v8:11460
Change-Id: Ib9243c1ed3c0cf8f5effd6d9b321f92367ca92e7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2783671
Commit-Queue: Shu-yu Guo <syg@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73789}

BUILD.gn

@@ -333,7 +333,7 @@ if (v8_enable_pointer_compression == "") {
       v8_current_cpu == "arm64" || v8_current_cpu == "x64"
 }
 if (v8_enable_pointer_compression_shared_cage == "") {
-  v8_enable_pointer_compression_shared_cage = v8_enable_pointer_compression
+  v8_enable_pointer_compression_shared_cage = false
 }
 if (v8_enable_fast_torque == "") {
   v8_enable_fast_torque = v8_enable_fast_mksnapshot