Settings: Duplicate device product strings for desktop

Defines string variants for the "desktop" product type which are simply
copies of the "device" string variants for now. This will decouple
desktop from the "device" product type, avoid using any "default"
strings (phone) in desktop, and allow for string overlay from RRO.

The desktop string variants have been reviewed by a UX writer (see
design doc in bug).

Bug: 392650416
Test: Manually verify UI strings
Flag: EXEMPT desktop only change
Change-Id: Ib8cc10d1886c253ee194f66bd46815f179940725