Make FileSystemAccess APIs consume user activation

User activation is consumed in the browser process instead of the
renderer process like input.showPicker() because consuming user
activation in the renderer would make the existing user activation check
in the browser process fail.

There is no browsertest because content::EvalJs() sets user activation
after running script, even with the flag to not run user activation, and
I don't know how to make it stop.

There is no web_test because consuming user activation in the browser
process does not notify the renderer process that it lost user
activation. It does not look like there is any existing interface to
make the browser tell the renderer that it lost user activation, only
the other way around.

I manually verified that the attached bug is fixed.

Spec issue: https://github.com/WICG/file-system-access/issues/458

Fixed: 40059071
Change-Id: Ia1f5ff63a8bdf6cdec70dea1406e9865123f96a5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5735618
Reviewed-by: Mustaq Ahmed <mustaq@chromium.org>
Reviewed-by: Fergal Daly <fergal@chromium.org>
Commit-Queue: Joey Arhar <jarhar@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1448885}