Enable `WEB_SEARCH` intent support to be handled by SearchActivity.

SearchActivity always supported external intents that included pre-set
Search Query. This change merely expands that coverage from explicit,
Chrome-targeting intents, to include Intent.ACTION_WEB_SEARCH.

WEB_SEARCH intents will by default open in SearchActivity, presenting
the user with the choice to execute, amend, or abandon the query
before it is executed.

Because this is controlled by a manifest flag, this can not be easily
controlled via flags.

Test: am start -a android.intent.action.WEB_SEARCH --es query Android

Bug: b:40800582
Change-Id: Ibf7db98be33bc258185028570d13b871368a0da2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6073387
Reviewed-by: Ted Choc <tedchoc@chromium.org>
Commit-Queue: Tomasz Wiszkowski <ender@google.com>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1393171}