Extension refactor (#20305)

This contains the main changes to the extensions crate from #20049. The
primary goal here is removing dependencies that we can't include on the
remote.


Release Notes:

- N/A

---------

Co-authored-by: Mikayla <mikayla@zed.dev>
Co-authored-by: Marshall Bowers <elliott.codes@gmail.com>
Co-authored-by: Marshall <marshall@zed.dev>

crates/zed/src/main.rs

@@ -7,6 +7,7 @@ mod reliability;
 mod zed;
 
 use anyhow::{anyhow, Context as _, Result};
+use assistant_slash_command::SlashCommandRegistry;
 use chrono::Offset;
 use clap::{command, Parser};
 use cli::FORCE_CLI_MODE_ENV_VAR_NAME;
@@ -23,6 +24,7 @@ use gpui::{
     VisualContext,
 };
 use http_client::{read_proxy_from_env, Uri};
+use indexed_docs::IndexedDocsRegistry;
 use language::LanguageRegistry;
 use log::LevelFilter;
 use reqwest_client::ReqwestClient;
@@ -39,6 +41,7 @@ use settings::{
 };
 use simplelog::ConfigBuilder;
 use smol::process::Command;
+use snippet_provider::SnippetRegistry;
 use std::{
     env,
     fs::OpenOptions,
@@ -402,12 +405,19 @@ fn main() {
             app_state.client.telemetry().clone(),
             cx,
         );
+        let api = extensions_ui::ConcreteExtensionRegistrationHooks::new(
+            ThemeRegistry::global(cx),
+            SlashCommandRegistry::global(cx),
+            IndexedDocsRegistry::global(cx),
+            SnippetRegistry::global(cx),
+            app_state.languages.clone(),
+            cx,
+        );
         extension_host::init(
+            api,
             app_state.fs.clone(),
             app_state.client.clone(),
             app_state.node_runtime.clone(),
-            app_state.languages.clone(),
-            ThemeRegistry::global(cx),
             cx,
         );
         recent_projects::init(cx);