buttons: Set min-width of button groups and icon buttons

This was initially changed to 80px in
I8e6beaf12d7cf1f1af20f4ff144eb0a7c2667a47
and then to 70px because 80px was too large for mobile in
I00b44508e7783957a8c24c4890cc1ba4dfe265da

Buttons inside button groups and icon buttons have a requirement
of being narrower than that but not narrower than their height.

When pseudo element css is not supported icons need a min-width

Bug: 71248
Change-Id: Icf45b9c8800067d3e30f23bbda4a6de21b1289d1
Merge "buttons: Set min-width of button groups and icon buttons"