zlog: Init (#27273)

Scaffolding for a revised way of logging in Zed. Very WIP, but the idea
is to allow maintainers to tell users to paste
```json
{
    "log": {
        "project.format": "trace"
    }
}
```
into their settings so that even trace logs are emitted for the log
statements emitted from a logger under the `project.format` scope.

The plan is to eventually implement the `Log` trait from the `log` crate
instead of just wrapping the `log` crate, which will simplify the
implementation greatly, and remove our need for both the `env_logger`
and `simplelog` crates.
Additionally, work will be done to transition to using the scoped
logging APIs throughout the app, focusing on bug hotspots to start
(currently, scoped logging is only used in the format codepath).

Release Notes:

- N/A

crates/zlog_settings/Cargo.toml

@@ -0,0 +1,23 @@
+[package]
+name = "zlog_settings"
+version = "0.1.0"
+edition.workspace = true
+publish.workspace = true
+license = "GPL-3.0-or-later"
+
+[lints]
+workspace = true
+
+[lib]
+path = "src/zlog_settings.rs"
+
+[features]
+default = []
+
+[dependencies]
+anyhow.workspace = true
+gpui.workspace = true
+schemars.workspace = true
+serde.workspace = true
+settings.workspace = true
+zlog.workspace = true

crates/zlog_settings/LICENSE-GPL

@@ -0,0 +1 @@
+../../LICENSE-GPL

crates/zlog_settings/src/zlog_settings.rs

@@ -0,0 +1,35 @@
+//! # zlog_settings
+use anyhow::Result;
+use gpui::App;
+use schemars::JsonSchema;
+use serde::{Deserialize, Serialize};
+use settings::{Settings, SettingsStore};
+
+pub fn init(cx: &mut App) {
+    ZlogSettings::register(cx);
+
+    cx.observe_global::<SettingsStore>(|cx| {
+        let zlog_settings = ZlogSettings::get_global(cx);
+        zlog::scope_map::refresh(&zlog_settings.scopes);
+    })
+    .detach();
+}
+
+#[derive(Clone, Debug, Default, Serialize, Deserialize, PartialEq, Eq, JsonSchema)]
+pub struct ZlogSettings {
+    #[serde(default, flatten)]
+    pub scopes: std::collections::HashMap<String, String>,
+}
+
+impl Settings for ZlogSettings {
+    const KEY: Option<&'static str> = Some("log");
+
+    type FileContent = Self;
+
+    fn load(sources: settings::SettingsSources<Self::FileContent>, _: &mut App) -> Result<Self>
+    where
+        Self: Sized,
+    {
+        sources.json_merge()
+    }
+}