Problems with theme font size (high DPI)) after upgrading to ST 3127+

After upgrading to ST 3128 (April 12th 2017), the theme font size doubled, resulting in huge letters for tab titles and in the side bar.

This is probably related to ST rolling out full support for High DPI themes in 3127. They also released [full documentation on writing themes](http://www.sublimetext.com/docs/3/themes.html), which might be useful.

Here is a quick screenshot of the resulting font sizes:

This was seen on both my MBP retina screen as on a 4k screen running in high DPI (aka retina, 1920x1024) mode. I did not have a non-retina screen available to compare with.

The issue reports a high-DPI theme font-size regression after upgrading to ST 3127+ and includes a screenshot plus a link to Sublime Text theme documentation. Start by reproducing it on the reported Retina/high-DPI displays and compare tab-title and sidebar sizes; done means those sizes no longer double after the upgrade.

Written by the indexing model from the issue text.