Scanning: Add material design styles to "Scan to" select element

Screenshot: http://shortn/_BdvyNYw4ov

Bug: 1059779
Test: browser_tests --gtest_filter=ScanningAppBrowserTest.All
Change-Id: I1433ac215c770c9f30e043b77345b371a0d93d2d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2517902Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Commit-Queue: Michael Checo <michaelcheco@google.com>
Cr-Commit-Position: refs/heads/master@{#824144}

chromeos/components/scanning/resources/scan_to_select.html

+<style include="scanning-shared"></style>
 <scan-settings-section>
   <span id="scanToLabel" slot="label">[[i18n('scanToDropdownLabel')]]</span>
   <div slot="settings">