assistant: Allow drag&dropping files/tabs into assistant panel (#17415)

This adds ability to the assistant panel's context editor to accept
files being dropped on it.

Multiple things can be dropped on the assistant panel:
- project panel entries (one or many)
- tabs (one)
- external files (one or many)


Release Notes:

- N/A


Demo:



https://github.com/user-attachments/assets/fddee751-cbdf-4e2c-ac80-35dfb857cc8a

Co-authored-by: Bennet <bennet@zed.dev>

crates/assistant/src/assistant.rs

@@ -27,8 +27,8 @@ use context_servers::ContextServerRegistry;
 pub use context_store::*;
 use feature_flags::FeatureFlagAppExt;
 use fs::Fs;
-use gpui::Context as _;
 use gpui::{actions, AppContext, Global, SharedString, UpdateGlobal};
+use gpui::{impl_actions, Context as _};
 use indexed_docs::IndexedDocsRegistry;
 pub(crate) use inline_assistant::*;
 use language_model::{
@@ -45,6 +45,7 @@ use slash_command::{
     file_command, now_command, project_command, prompt_command, search_command, symbols_command,
     tab_command, terminal_command, workflow_command,
 };
+use std::path::PathBuf;
 use std::sync::Arc;
 pub(crate) use streaming_diff::*;
 use util::ResultExt;
@@ -70,6 +71,14 @@ actions!(
     ]
 );
 
+#[derive(PartialEq, Clone, Deserialize)]
+pub enum InsertDraggedFiles {
+    ProjectPaths(Vec<PathBuf>),
+    ExternalFiles(Vec<PathBuf>),
+}
+
+impl_actions!(assistant, [InsertDraggedFiles]);
+
 const DEFAULT_CONTEXT_LINES: usize = 50;
 
 #[derive(Copy, Clone, Debug, Eq, PartialEq, PartialOrd, Ord, Hash, Serialize, Deserialize)]