In addition to what you did, I also added the custom font to client\dist\jimu-ui\index.js (I am running ExB Developer Edition version 1.12). So for your font, you would have a string in that index.js file similar to:
function(e){e.PETRONA="Petrona",e.AVENIRNEXT="Avenir Next",e.CALIBRI="Calibri",e.PMINGLIU="PmingLiu",e.IMPACT="Impact",e.GEORGIA="Georgia",e.ARIAL="Arial",e.TIMESNEWROMAN="Times New Roman",e.SIMHEI="SimHei",e.MICROSOFTYAHEI="Microsoft YaHei"}
Finally, I also added it to: \client\dist\jimu-ui\advanced\rich-text-editor.js
So you would have a string in that rich-text-editor.js file similar to:
const p=[d.FontFamilyValue.PETRONA,d.FontFamilyValue.AVENIRNEXT,d.FontFamilyValue.CALIBRI,d.FontFamilyValue.PMINGLIU,d.FontFamilyValue.IMPACT,d.FontFamilyValue.GEORGIA,d.FontFamilyValue.ARIAL,d.FontFamilyValue.TIMESNEWROMAN,d.FontFamilyValue.SIMHEI,d.FontFamilyValue.MICROSOFTYAHEI]
I believe that string shows up twice in rich-text-editor.js so make sure you update both.
Hopefully this does the trick!