[iOS] Fixing Invocation of handler when UITrait changes

This CL fixes an RBS crash that occurs when a user modifies one of the
observed UITraits when they are browsing their password credential
provider.

The crash was caused by the system passing in a UITraitEnvironment
object when a UITraitCollection was expected. This CL fixes this issue
because now the previous trait collection is explicitly passed to the
callback function, ensuring correctness.

Fixed: 377755242
Change-Id: I8faecf5d002f032497ff113eb4b95b261b06c241
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6072838
Commit-Queue: Daniel White <danieltwhite@google.com>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1394901}