lang/lua53: update to 5.3.6

This release fixes all bugs listed here: https://www.lua.org/bugs.html#5.3.5

While we're here, do some cleanup work in preparation for an impending
lang/lua54 port:

• Various reordering to appease portclippy
• The patch to src/Makefile has been renamed to match the standard naming convention since it was relatively close
• Use ${LUA_VER_STR} in place of again writing out the version string
• Use various LUA_* substitutions in the plist to reduce change on new versions

The latter two have actually been backported from the submitted lua54 port
in D14709, rather than being included in the original submission, to make
the diff between lang/lua53 and lang/lua54 more obvious.

Submitted by: Russ Haley <russ haley gmail com>
Submitted with: Andrew Gierth <andrew_tao173 riddles org uk>
Differential Revision: https://reviews.freebsd.org/D25797