initial version of CFF/CFF2 profile with checks for max call depth

[cjchapman]

Description

This PR represents the start of a CFF/CFF2 profile (which is included in the opentype profile) with two new checks that traverse the CFF or CFF2 subroutine call tree to ensure that the max call depth of 10 is not exceeded:

• com.adobe.fonts/check/cff_call_depth Is the CFF subr/gsubr call depth > 10?
• com.adobe.fonts/check/cff2_call_depth Is the CFF2 subr/gsubr call depth > 10?

also included are CFF and CFF2 test fonts with glyphs that have varying call depths, specifically:

'B' -- max call depth: 9
'C' -- max call depth: 10
'D' -- max call depth: 11
'E' -- max call depth: 12
'F' -- calls a gsubr that calls itself for infinite recursion

To Do

• update CHANGELOG.md
• wait for checks to pass (except github/pages, which is stuck)
• request a review

[felipesanches]

This looks really good :-)

I will try to merge this after merging #2426