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/src/wasm_host/wit.rs

@@ -262,11 +262,11 @@ impl Extension {
         &self,
         store: &mut Store<WasmState>,
         command: &SlashCommand,
-        query: &str,
+        arguments: &[String],
     ) -> Result<Result<Vec<SlashCommandArgumentCompletion>, String>> {
         match self {
             Extension::V010(ext) => {
-                ext.call_complete_slash_command_argument(store, command, query)
+                ext.call_complete_slash_command_argument(store, command, arguments)
                     .await
             }
             Extension::V001(_) | Extension::V004(_) | Extension::V006(_) => Ok(Ok(Vec::new())),
@@ -277,12 +277,12 @@ impl Extension {
         &self,
         store: &mut Store<WasmState>,
         command: &SlashCommand,
-        argument: Option<&str>,
+        arguments: &[String],
         resource: Option<Resource<Arc<dyn LspAdapterDelegate>>>,
     ) -> Result<Result<SlashCommandOutput, String>> {
         match self {
             Extension::V010(ext) => {
-                ext.call_run_slash_command(store, command, argument, resource)
+                ext.call_run_slash_command(store, command, arguments, resource)
                     .await
             }
             Extension::V001(_) | Extension::V004(_) | Extension::V006(_) => {