gpui: Further docs refinement & moved some reexports into 'private' module (#3935)

This commit mostly fixes invalid URLs in docstrings. It also
encapsulates crates we reexport (serde stuff + linkme) into a public
module named "private" in order to reduce the API surfaced through docs.
Moreover, I fixed up a bunch of crates that were pulling serde_json in
through gpui explicitly instead of using Cargo manifest.

Release Notes:
- N/A

crates/theme_importer/Cargo.toml

@@ -18,6 +18,7 @@ palette = { version = "0.7.3", default-features = false, features = ["std"] }
 pathfinder_color = "0.5"
 rust-embed.workspace = true
 serde.workspace = true
+serde_json.workspace = true
 simplelog = "0.9"
 strum = { version = "0.25.0", features = ["derive"] }
 theme = { path = "../theme", features = ["importing-themes"] }

crates/theme_importer/src/main.rs

@@ -16,7 +16,6 @@ use any_ascii::any_ascii;
 use anyhow::{anyhow, Context, Result};
 use clap::Parser;
 use convert_case::{Case, Casing};
-use gpui::serde_json;
 use indexmap::IndexMap;
 use indoc::formatdoc;
 use json_comments::StripComments;

crates/theme_importer/src/zed1/converter.rs

@@ -1,5 +1,5 @@
 use anyhow::{Context, Result};
-use gpui::{serde_json, Hsla, Rgba};
+use gpui::{Hsla, Rgba};
 use theme::{
     color_alpha, Appearance, PlayerColor, PlayerColors, StatusColorsRefinement,
     ThemeColorsRefinement, UserFontStyle, UserFontWeight, UserHighlightStyle, UserSyntaxTheme,

crates/theme_importer/src/zed1/theme.rs

@@ -6,10 +6,10 @@ use std::fmt;
 use std::ops::{Deref, DerefMut};
 use std::sync::Arc;
 
-use gpui::serde_json::{self, Value};
 use pathfinder_color::ColorU;
 use serde::de::{self, DeserializeOwned, Unexpected};
 use serde::{Deserialize, Deserializer};
+use serde_json::{self, Value};
 
 #[derive(Clone, Copy, Default, PartialEq, Eq, Hash, PartialOrd, Ord)]
 #[repr(transparent)]