renderer/metal: handle preedit wider than our screen

src/renderer/Metal.zig

@@ -1101,10 +1101,9 @@ fn rebuildCells(
         y: usize,
         x: [2]usize,
     } = if (preedit) |preedit_v| preedit: {
-        var x = screen.cursor.x;
         break :preedit .{
             .y = screen.cursor.y,
-            .x = .{ x, x + preedit_v.width() },
+            .x = preedit_v.range(screen.cursor.x, screen.cols - 1),
         };
     } else null;
 

src/renderer/State.zig

@@ -48,4 +48,12 @@ pub const Preedit = struct {
 
         return result;
     }
+
+    pub fn range(self: *const Preedit, start: usize, max: usize) [2]usize {
+        // If our preedit goes off the end of the screen, we adjust it so
+        // that it shifts left.
+        const end = start + self.width();
+        const offset = if (end > max) end - max else 0;
+        return .{ start -| offset, end -| offset };
+    }
 };