Add yank-handled-properties; use it for `font-lock-face' and `category'
properties, instead of hard-coding these properties' special handling.
* lisp/simple.el (yank-handled-properties): New defcustom.
(yank-excluded-properties): Add font-lock-face and category.
(yank): Doc fix.
* lisp/subr.el (remove-yank-excluded-properties): Obey
yank-handled-properties. The special handling of font-lock-face
and category is now done this way, instead of being hard-coded.
(insert-for-yank-1): Remove font-lock-face handling.
(yank-handle-font-lock-face-property)
(yank-handle-category-property): New function.