Pad ime_switcher same as navbar buttons

Use same padding value (@dimen/navigation_side_padding) for ime_switcher width
as for other navbar buttons. This corrects the alignment of the ime_switcher
button on the navbar, giving it the same width as other navbar buttons (e.g.
clipboard, or custom key) for a more symmetric look.

Ticket: #1475
Test: m, check layout on device/tablet
Change-Id: I5d96ce1b18a43d4788d15d54568e638328c4fbc3