[lens] Add <webview> results behind a flag

This CL introduces a <webview> to host the results remote UI instead of
an iframe. This is a preliminary step to be able to start diagnosing
issues. All behind a default off flag.

Bug: 441582782

Change-Id: Id5933f6ab5970242cc9719a42c35d4a379e38719
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6893251
Reviewed-by: Tim <tjudkins@chromium.org>
Reviewed-by: Alex Gough <ajgo@chromium.org>
Reviewed-by: Juan Mojica <juanmojica@google.com>
Commit-Queue: Duncan Mercer <mercerd@google.com>
Cr-Commit-Position: refs/heads/main@{#1508433}