Plus Button (3/3): wire feature into drawer + main panel tab strips

Gate `createTabbedLocation`'s plus-button install and the drawer's
legacy three-dot more-tabs button on `hostConfig.devToolsPlusButton`
so the panel tab strip and the drawer get the plus button when the
`DevToolsPlusButton` base::Feature is enabled.

- ViewManager: install the plus button before `appendApplicableItems`
  so the first layout pass reserves its width.
- InspectorDrawerView: drop the legacy more-tabs button when the plus
  button is on; hide the slotted button when the drawer is vertically
  minimized via the existing `.hide-element` container.
- Distinguish jslog contexts per surface
  (`plus-button-panel` / `plus-button-drawer`) and register both in
  `KnownContextValues`.
- Add unit tests for symmetric same-titled-tab dedup and the
  vertical-minimized hide, plus an e2e suite covering both surfaces
  and the per-surface jslog assertion.

Related:
  Prototype: https://crrev.com/c/7792390
  CL1: https://crrev.com/c/7814020
  CL2: https://crrev.com/c/7846805
  Chromium enum: https://crrev.com/c/7853628
  Chromium feature param: https://crrev.com/c/7857037
  Chromium flags: https://crrev.com/c/7883967

Bug: 506004822
Change-Id: I258f1188ab334149b8414c7855390d1c7f1a96df
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/7882040
Reviewed-by: Wolfgang Beyer <wolfi@chromium.org>
Reviewed-by: Danil Somsikov <dsv@chromium.org>
Commit-Queue: Guangyue Xu <guangyue.xu@microsoft.com>