Revert "Temporarily disable frozen/sealed elements kinds"

This reverts commit 05d83a0e.

Reason for revert: We passed the M78 branch point and should proceed testing
the new elements kinds support.

Original change's description:
> Temporarily disable frozen/sealed elements kinds
>
> ... to prepare for merging this back to stable channel.
>
> Bug: chromium:992914
> Change-Id: Icbb257b5c02417d9222e60346575567360376264
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1762021
> Reviewed-by: Leszek Swirski <leszeks@chromium.org>
> Commit-Queue: Leszek Swirski <leszeks@chromium.org>
> Auto-Submit: Igor Sheludko <ishell@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#63277}

TBR=leszeks@chromium.org,ishell@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: chromium:992914, v8:996176
Change-Id: Iaa36c140c0c9c72ca0e58f5c3e7d4cad67027085
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1795342Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63653}

src/flags/flag-definitions.h

@@ -391,7 +391,7 @@ DEFINE_BOOL(enable_one_shot_optimization, true,
             "only be executed once")
 
 // Flag for sealed, frozen elements kind instead of dictionary elements kind
-DEFINE_BOOL_READONLY(enable_sealed_frozen_elements_kind, false,
+DEFINE_BOOL_READONLY(enable_sealed_frozen_elements_kind, true,
                      "Enable sealed, frozen elements kind")
 
 // Flags for data representation optimizations