chromeos: Move SVG icons for OS settings to chromeos/os_icons.html

The go/splitsettings project is moving Chrome OS settings to a new
WebUI settings surface. Migrate the OS icons into their own file.
This reduces the number of <if> conditions in settings/icons.html
and makes it clearer these are Chrome OS-only.

Use viewBox to avoid having separate os-settings20 and os-settings24
iconsets.

I have a request out to UX to re-export the SVGs at 20 pixels so we
don't need to use viewBox anymore.

Screenshots, just to illustrate that nothing changed:

Chrome OS combined: http://screen/ipZ38gvF1S1
SplitSettings OS: http://screen/VXoRW8y16eR
SplitSettings browser: http://screen/0nqDyMMt2qg
Linux: http://screen/j91ivK0YigV

Bug: 990394
Change-Id: Ica5976d5b4650b191ea1746e3f7b41983a2ca45d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1733465
Commit-Queue: James Cook <jamescook@chromium.org>
Reviewed-by: Tommy Li <tommycli@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684023}
21 files changed