[Request] Add dollar sign ($) as a non-standard symbol

The games Sonic Robo Blast 2 and Sonic Robo Blast 2 Kart use the dollar sign symbol for a sort of replacement for assignment operators.

Example 1

local a = 1
a = $ | 2

is equivalent to

local a = 1
a = a | 2

Example 2

local tbl = {
    a = 1
}
tbl.a = $ | 2

is equivalent to

local tbl = {
    a = 1
}
tbl.a = tbl.a | 2

Example 3

playerMo.flags = $ & ~MF_NOGRAVITY

is equivalent to

playerMo.flags = playerMo.flags & ~MF_NOGRAVITY

issue 中没有指定源文件或测试。首先定位 Lua 表达式的 parser 或语法分析入口点，并将其与三个示例进行比较；当带美元符号的形式能够被接受，并像所示的自引用表达式一样处理，同时不破坏标准 Lua 语法时，即表示完成。