Feature/fallback fonts (#15306)

Supersedes https://github.com/zed-industries/zed/pull/12090

fixes #5180
fixes #5055

See original PR for an example of the feature at work.

This PR changes the settings interface to be backwards compatible, and
adds the `ui_font_fallbacks`, `buffer_font_fallbacks`, and
`terminal.font_fallbacks` settings.

Release Notes:

- Added support for font fallbacks via three new settings:
`ui_font_fallbacks`, `buffer_font_fallbacks`, and
`terminal.font_fallbacks`.(#5180, #5055).

---------

Co-authored-by: Junkui Zhang <364772080@qq.com>

crates/gpui/Cargo.toml

@@ -93,6 +93,7 @@ cbindgen = { version = "0.26.0", default-features = false }
 block = "0.1"
 cocoa.workspace = true
 core-foundation.workspace = true
+core-foundation-sys = "0.8"
 core-graphics = "0.23"
 core-text = "20.1"
 foreign-types = "0.5"