Allow extensions to define providers for indexing docs (#13755)

This PR provides extensions with the ability to define providers for
indexing docs.

Release Notes:

- N/A

crates/extension_api/src/extension_api.rs

@@ -27,7 +27,7 @@ pub use wit::{
     zed::extension::platform::{current_platform, Architecture, Os},
     zed::extension::slash_command::{SlashCommand, SlashCommandOutput, SlashCommandOutputSection},
     CodeLabel, CodeLabelSpan, CodeLabelSpanLiteral, Command, DownloadedFileType, EnvVars,
-    LanguageServerInstallationStatus, Range, Worktree,
+    KeyValueStore, LanguageServerInstallationStatus, Range, Worktree,
 };
 
 // Undocumented WIT re-exports.
@@ -127,6 +127,15 @@ pub trait Extension: Send + Sync {
     ) -> Result<SlashCommandOutput, String> {
         Err("`run_slash_command` not implemented".to_string())
     }
+
+    fn index_docs(
+        &self,
+        _provider: String,
+        _package: String,
+        _database: &KeyValueStore,
+    ) -> Result<(), String> {
+        Err("`index_docs` not implemented".to_string())
+    }
 }
 
 /// Registers the provided type as a Zed extension.
@@ -249,6 +258,14 @@ impl wit::Guest for Component {
     ) -> Result<SlashCommandOutput, String> {
         extension().run_slash_command(command, argument, worktree)
     }
+
+    fn index_docs(
+        provider: String,
+        package: String,
+        database: &KeyValueStore,
+    ) -> Result<(), String> {
+        extension().index_docs(provider, package, database)
+    }
 }
 
 /// The ID of a language server.