vc-ui: Extract the vcui TitleView from the feature flag

Extract the vcui TitleView from the VCTrayTitleHeader flag so the title
header will be enabled by default. It should be safe because it only
adds UI elements like an icon and a text, without any functionality.

But still use the VCTrayTitleHeader flag for the sidetone, so we can
still run the same finch experiment.

Bug: 365908163
Change-Id: I6c7364d8a999dea013785aa3d234a173d625e46c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5856819
Reviewed-by: Andre Le <leandre@chromium.org>
Auto-Submit: Norman Bintang <normanbt@chromium.org>
Reviewed-by: Li-Yu Yu <aaronyu@google.com>
Commit-Queue: Andre Le <leandre@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1355323}