[iOS] Add ChooseFileControllerImpl instantiated by RunOpenPanel

This CL adds the class ChooseFileControllerImpl which implements the
abstract class ChooseFileController so it can be instantiated when
RunOpenPanel is called on ChooseFileTabHelper.

Bug: 441659098
Change-Id: I9981f0ee2a7503df7d287717f6e352102f76baba
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7006355
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Commit-Queue: Quentin Pubert <qpubert@google.com>
Auto-Submit: Quentin Pubert <qpubert@google.com>
Cr-Commit-Position: refs/heads/main@{#1526811}