Further improve /tabs command and slash arguments completion (#16216)

* renames `/tabs` to `/tab`
* allows to insert multiple tabs when fuzzy matching by the names
* improve slash command completion API, introduce a notion of multiple
arguments
* properly fire off commands on arguments' completions with
`run_command: true`

Release Notes:

- N/A

---------

Co-authored-by: Marshall Bowers <marshall@zed.dev>

crates/extension_api/src/extension_api.rs

@@ -114,7 +114,7 @@ pub trait Extension: Send + Sync {
     fn complete_slash_command_argument(
         &self,
         _command: SlashCommand,
-        _query: String,
+        _args: Vec<String>,
     ) -> Result<Vec<SlashCommandArgumentCompletion>, String> {
         Ok(Vec::new())
     }
@@ -123,7 +123,7 @@ pub trait Extension: Send + Sync {
     fn run_slash_command(
         &self,
         _command: SlashCommand,
-        _argument: Option<String>,
+        _args: Vec<String>,
         _worktree: Option<&Worktree>,
     ) -> Result<SlashCommandOutput, String> {
         Err("`run_slash_command` not implemented".to_string())
@@ -257,17 +257,17 @@ impl wit::Guest for Component {
 
     fn complete_slash_command_argument(
         command: SlashCommand,
-        query: String,
+        args: Vec<String>,
     ) -> Result<Vec<SlashCommandArgumentCompletion>, String> {
-        extension().complete_slash_command_argument(command, query)
+        extension().complete_slash_command_argument(command, args)
     }
 
     fn run_slash_command(
         command: SlashCommand,
-        argument: Option<String>,
+        args: Vec<String>,
         worktree: Option<&Worktree>,
     ) -> Result<SlashCommandOutput, String> {
-        extension().run_slash_command(command, argument, worktree)
+        extension().run_slash_command(command, args, worktree)
     }
 
     fn suggest_docs_packages(provider: String) -> Result<Vec<String>, String> {

crates/extension_api/wit/since_v0.1.0/extension.wit

@@ -130,10 +130,10 @@ world extension {
     export labels-for-symbols: func(language-server-id: string, symbols: list<symbol>) -> result<list<option<code-label>>, string>;
 
     /// Returns the completions that should be shown when completing the provided slash command with the given query.
-    export complete-slash-command-argument: func(command: slash-command, query: string) -> result<list<slash-command-argument-completion>, string>;
+    export complete-slash-command-argument: func(command: slash-command, args: list<string>) -> result<list<slash-command-argument-completion>, string>;
 
     /// Returns the output from running the provided slash command.
-    export run-slash-command: func(command: slash-command, argument: option<string>, worktree: option<borrow<worktree>>) -> result<slash-command-output, string>;
+    export run-slash-command: func(command: slash-command, args: list<string>, worktree: option<borrow<worktree>>) -> result<slash-command-output, string>;
 
     /// Returns a list of packages as suggestions to be included in the `/docs`
     /// search results.