Moves the strings for the "Homepage" and "Firefox Home" sections of
about:settings#home into newtab.ftl, so they ship in the newtab XPI
alongside AboutPreferences.sys.mjs.
Strings shared with the legacy settings renderer get "-srd" suffix
copies in newtab.ftl with the redesigned code rewired, so the two files
don't define the same IDs.
Differential Revision: https://phabricator.services.mozilla.com/D301718