[HarfBuzz] 'mark' feature in myanmar

[Jonathan Kew]

Hey Behdad,

In hb-ot-shape-complex-myanmar.cc, we have the code fragment

   /*
    * Note:
    *
    * Spec says 'mark' is used, and the mmrtext.ttf font from
    * Windows 8 has lookups for it.  But testing suggests that
    * Windows 8 Uniscribe is NOT applying it.  It *is* applying
    * 'mkmk' however.
    */
   if (hb_options ().uniscribe_bug_compatible)
     plan->map.add_feature (HB_TAG('m','a','r','k'), 0, F_GLOBAL);

which disables the 'mark' feature in Uniscribe-compatible mode.

However, AFAICT from my current testing, it looks like Uniscribe on Win8 
*is* applying the 'mark' feature, and so this is resulting in tons of 
unwanted discrepancies when I try to compare stuff. (This is when 
testing with the mmrtext.ttf font from Windows 8.)

Could you re-test and see whether you agree that 'mark' is now being 
applied by Uniscribe? (I wonder if there's been a fix in a Win8 update 
of some kind since we originally worked on this?) If so, we should 
remove this hack.

JK