Merge StoreFixedDoubleArrayElementSmi into StoreFixedDoubleArrayElement.

Bug: v8:9708, v8:6949
Change-Id: If82893e16117362b40219bbe768acfc94be498e5
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2377949Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69574}