[Lua] Split out = from other operators

[mbartlett21]

The syntax now handles multi-global statements correctly and also makes attributes only apply in local statements. It also marks some other things as invalid in local statements.

    a, b = c, d
--   ^ punctuation.separator.comma
--          ^ punctuation.separator.comma


    globals_no_modifiers <const> 7
--                       ^ keyword.operator.comparison.lua
--                        ^^^^^ variable.other.lua
--                             ^ keyword.operator.comparison.lua

    local a + b
--          ^ invalid