[heap] Enable usage of ArrayBufferExtensions

Switch the flag to true to enable ArrayBufferExtensions by default. The
last CL (https://crrev.com/c/2065088) that tried to enable this was
reverted because of alignment issues on ARM64
(fixed in https://crrev.com/c/2071256).

Bug: v8:10064
Change-Id: I47f478c978094fb5038113eb452865748956b42e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2074157Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Dominik Inführ <dinfuehr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66460}

BUILD.gn

@@ -128,7 +128,7 @@ declare_args() {
   v8_enable_concurrent_marking = true
 
   # Sets -dV8_ARRAY_BUFFER_EXTENSION
-  v8_enable_array_buffer_extension = false
+  v8_enable_array_buffer_extension = true
 
   # Enables various testing features.
   v8_enable_test_features = ""