Select applicable positions for lsp_ext methods more leniently (#32272)

Closes https://github.com/zed-industries/zed/issues/27238

Release Notes:

- Fixed `editor::SwitchSourceHeader` and
`editor::ExpandMacroRecursively` not working with text selections

crates/editor/src/lsp_ext.rs

@@ -42,8 +42,8 @@ where
         .selections
         .disjoint_anchors()
         .iter()
-        .filter(|selection| selection.start == selection.end)
-        .filter_map(|selection| Some((selection.start, selection.start.buffer_id?)))
+        .filter_map(|selection| Some((selection.head(), selection.head().buffer_id?)))
+        .unique_by(|(_, buffer_id)| *buffer_id)
         .filter_map(|(trigger_anchor, buffer_id)| {
             let buffer = editor.buffer().read(cx).buffer(buffer_id)?;
             let language = buffer.read(cx).language_at(trigger_anchor.text_anchor)?;
@@ -53,7 +53,6 @@ where
                 None
             }
         })
-        .unique_by(|(_, buffer, _)| buffer.read(cx).remote_id())
         .collect::<Vec<_>>();
 
     let applicable_buffer_tasks = applicable_buffers

crates/editor/src/rust_analyzer_ext.rs

@@ -132,9 +132,6 @@ pub fn expand_macro_recursively(
     window: &mut Window,
     cx: &mut Context<Editor>,
 ) {
-    if editor.selections.count() == 0 {
-        return;
-    }
     let Some(project) = &editor.project else {
         return;
     };