Add slow fontmake compile time projects for testing

[chrissimpkins]

Thread to collect information on open projects that have slow fontmake-based compile times so that we can reproduce the compile during diagnostic and optimization tests.

Let's consider "slow" to be over 10 minutes wall clock time to start. Please feel free to suggest a different time if this is not a good arbitrary target to begin. (We're going to examine the distribution of Fonts compile times to better define what is "slow", #25)

Please include the following details:

• repository URL
• testing commit
• project requirements.txt file with Python dependency versions
• any information that you have on why the project might have slow source to font compile times

cc @marekjez86 @madig @simoncozens @belluzj

[chrissimpkins]

https://github.com/googlefonts/roboto-serif

@davelab6 mentioned to me today that this is might be a good example based on feedback from @m4rc1e.

154 master, 4 axis VF design space