[iOS][PinnedTabs] Blurs view background

This CL applies a blur effet on the pinned tabs view background.

Fixed: 1393025
Change-Id: I9b3f5ad3136feec536d03f0cf4055a30bfb297a7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4051083


Reviewed-by: Petro Akzhygitov <pakzhygitov@google.com>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Ewann Pellé <ewannpv@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1075567}