[Extensions] Show extension detail mv2 deprecation message for exp stage

Reland of crrev.com/c/5631987. Original CL was reverted because parent
crrev.com/c/5631965 had a failing test.

Fixed by:
Parent CL was fixed and re-landed, thus we can re-land this CL (without
any code changes).

Show a Manifest V2 deprecation message in the extension's detail page
for the experiment stage 2 (ExtensionManifestV2Disabled). This
includes:
  - Header and subtitle based on experiment stage
  - Find alternative button shown iff experiment stage #1
  - New remove button shown iff experiment stage #2

Screenshot (with ExtensionManifestV2Disabled flag enabled):
https://drive.google.com/file/d/1vm792y6RqXc9a97gZNpUSWXAuDqWEd1k/view?usp=sharing

Bug: 339061151
Change-Id: Ic1a6fe4eab6464d343293d14920a62da50d688a1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5645962
Commit-Queue: Emilia Paz <emiliapaz@chromium.org>
Reviewed-by: Kelvin Jiang <kelvinjiang@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1319867}