…ILD.gn file."

This reverts commit 306478860b1f3f23e10b6c4ad54436863bbce0c4.

Reason for revert: https://g-issues.chromium.org/issues/338220073

Original change's description:
> Split app_service/webapk into its own BUILD.gn file.
>
> This creates a new BUILD.gn file for app_service/webapk which is
> unidirectionally depended on by the App Service. As part of this,
> webapk_manager.{h,cc} is moved to the app_service directory as it
> depends on App Service, avoiding a dependency cycle.
>
> Bug: b/336172688
> Change-Id: I5f16ab2bcbf1c9ab91465fab53e13c20c5b6e228
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5495189
> Reviewed-by: Tim Sergeant <tsergeant@chromium.org>
> Commit-Queue: Dominick Ng <dominickn@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1294740}

(cherry picked from commit 6ae68471df328bbecc8eba7c9c834a6572ff9862)

Bug: b/336172688
Change-Id: Iece71b427bd1c57d086c12207ba26b8d75a5c29a
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5504734
Reviewed-by: Haiyang Pan <hypan@google.com>
Auto-Submit: Ian Wells <iwells@chromium.org>
Commit-Queue: Haiyang Pan <hypan@google.com>
Owners-Override: Ian Wells <iwells@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#1294922}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5508920
Reviewed-by: Krishna Govind <govind@chromium.org>
Owners-Override: Krishna Govind <govind@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/branch-heads/6452@{#4}
Cr-Branched-From: dc6e5f15f2f14a3206bcb9cf0297c3c73dc075b8-refs/heads/main@{#1294836}