feat(web): iPhone display problem with Tahoma font in touch layout

The Tahoma font is not available on iPhone, so when a keyboard specifying this font is used on an iPhone, a default Times New Roman style font is used and the result is "ugly". (See issue keymanapp/keyboards#1877 for details.) Manually changing the font to DejaVu Sans seems to fix the issue for a specific keyboard (see pull request keymanapp/keyboards#1921 for example).

Currently (2022-07) there are 115 keyboards in the repository still specifying Tahoma as the font to use for touch layout. @mcdurdin plans to handle this at a platform level. This is planned for Keyman version 17 as part of addressing theming across all platforms.