FilePicker: Allow setting an initial search query

This can be used to set an initial query from a register. Global
search will use this and the file picker could also consider allowing
an initial query using this helper.

helix-term/src/ui/picker.rs

@@ -150,6 +150,11 @@ impl<T: Item + 'static> FilePicker<T> {
         self
     }
 
+    pub fn with_line(mut self, line: String, editor: &Editor) -> Self {
+        self.picker.set_line(line, editor);
+        self
+    }
+
     fn current_file(&self, editor: &Editor) -> Option<FileLocation> {
         self.picker
             .selection()
@@ -679,6 +684,10 @@ impl<T: Item> Picker<T> {
         }
         EventResult::Consumed(None)
     }
+
+    pub fn set_line(&mut self, line: String, editor: &Editor) {
+        self.prompt.set_line(line, editor);
+    }
 }
 
 // process:

helix-term/src/ui/prompt.rs

@@ -87,11 +87,15 @@ impl Prompt {
     }
 
     pub fn with_line(mut self, line: String, editor: &Editor) -> Self {
+        self.set_line(line, editor);
+        self
+    }
+
+    pub fn set_line(&mut self, line: String, editor: &Editor) {
         let cursor = line.len();
         self.line = line;
         self.cursor = cursor;
         self.recalculate_completion(editor);
-        self
     }
 
     pub fn line(&self) -> &String {