core: preedit modification sets full screen dirty

Fixes #1735

src/Surface.zig

@@ -1089,6 +1089,9 @@ pub fn preeditCallback(self: *Surface, preedit_: ?[]const u8) !void {
         self.renderer_state.preedit = null;
     }
 
+    // Mark preedit dirty flag
+    self.io.terminal.flags.dirty.preedit = true;
+
     // If we have no text, we're done. We queue a render in case we cleared
     // a prior preedit (likely).
     const text = preedit_ orelse {

src/terminal/Terminal.zig

@@ -135,6 +135,9 @@ pub const Dirty = packed struct {
     /// Screen clear of some kind. This can be due to a screen change,
     /// erase display, etc.
     clear: bool = false,
+
+    /// Set when the pre-edit is modified.
+    preedit: bool = false,
 };
 
 /// The event types that can be reported for mouse-related activities.