Rework jit-lock-antiblink-grace after Stefan's comments
* lisp/jit-lock.el (jit-lock--antiblink-l-b-p): Rename from jit-lock--antiblink-l-l-b. (jit-lock--antiblink-grace-timer): Add period to docstring. (jit-lock--antiblink-post-command): Rework after Stefan's comments.