Fix misc CoreText rendering bugs and issues with clipping and composing characters#1356

ychin merged 4 commits intomacvim-dev:mastermacvim-dev/macvim:masterfrom

ychin:coretext-rendering-fixes-composing-chars-clippingychin/macvim:coretext-rendering-fixes-composing-chars-clippingCopy head branch name to clipboard