feature: support generics in function type format

Currently, the only way to document generic functions is to use @generic. and it's not possible to use them in overloads or fields.

The following examples are invalid:

---@generic T
---@param arg1 string
---@param arg2 T
---@return T
---@overload fun(arg2: T) <- Undefined type or alias `T`.
local function foo(arg1, arg2)
    return arg2 or arg1
end

---@class Foo
---@field bar fun<T>(arg:T): T <- `(` expected.
local Foo = {}

未指定源文件或测试。首先定位 @generic、@overload 和函数类型的解析与类型解析路径，然后将其与两个 Lua 示例进行比较。完成标准是：泛型类型参数能够在重载签名和字段函数类型中解析，且不出现报告中的诊断信息。