Global aliases cause performance regression

[danielshahaf]

I've compared the performance of 0.7.1 and current master (343ec10) using the make perf tool added in the referenced commit. I locally deleted all highlighters except main (to prevent their tests from running) and ran () { git checkout "$1" zsh-syntax-highlighting.plugin.zsh zsh-syntax-highlighting.zsh highlighters/main/main-highlighter.zsh } on various commits.

I found that 3c5f63d runs 27% more slowly than its parent, and 343ec1061fda6ecbc9782e33a8e4539525899594 runs 26% more slowly than 0.7.1. Furthermore, reverting that patch (one hunk conflicts, but I just ignored that) fixes the problem.