opentype language tags for core text renderer

apparently the Core text renderer supports activating language tags in advanced opentype fonts, https://en.wikipedia.org/wiki/Apple_Advanced_Typography

the iosevka font implements fancy ligatures on a per-programming-language basis using these language tags.
https://github.com/be5invis/Iosevka/issues/56
(see also the README of this repo for examples)
the atom editor supports this via the use of custom stylesheets afaiu.

i find this a saner solution than enabling a fixed set of ligatures globally for a gui font, since the set of ligatures that make sense depends on the programming language. for example, is <= an arrow or a comparison operator? does |> have a special meaning in the language? etc.

so, feature request: could MacVim allow setting language tags for the Core Text renderer in opentype gui fonts? ideally this would be a new setting that can be put into a filetype-specific autocommand.

首先定位 MacVim 的 Core Text 渲染器，以及请求中提到的 GUI 字体设置入口。跟踪文件类型专用的 autocommand 如何提供 OpenType 语言标签，并结合 Iosevka 示例和链接的参考资料确认预期行为。当一个有文档说明的设置能够在 Core Text 字体中按文件类型应用语言标签时，即表示完成。