Revert "[Code Health][iOS] Move ios/chrome/browser/web to model subfolder"

This reverts commit 34ec8f6a528daffeef175a276c5c5b457340853e.

Reason for revert: breaks build, as in https://ci.chromium.org/ui/p/chromium/builders/ci/ios-catalyst/95602/overview

Original change's description:
> [Code Health][iOS] Move ios/chrome/browser/web to model subfolder
>
> To simplify the folder hierarchy on iOS and have a clearer layer
> separation, all the files in ios/c/b/<foo>/ will be moved to
> ios/c/b/<foo>/model/ to showcase that they are model files.
>
> Make public dependency available for test and migrate it.
>
> Bug: 1480376
> Change-Id: Ib1cdc5ddec723303c6c014d2e798b5e4806ff207
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5089949
> Auto-Submit: Weizhong Xia <weizhong@google.com>
> Commit-Queue: Weizhong Xia <weizhong@google.com>
> Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1233984}

Bug: 1480376
Change-Id: I09e81f233e188571f0221906d6921645f766a0b7
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5096453
Owners-Override: Alan Screen <awscreen@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Alan Screen <awscreen@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1234020}