gui: ResetFontAndWindowSize should use known dpi

This code was partially replicating the initial window setup
where we didn't necessarily know the dpi, but in the context
where this is run, we do know the dpi for the window, so
let's consistently use that number throughout.

refs: #1039

wezterm-gui/src/termwindow/resize.rs

@@ -327,7 +327,7 @@ impl super::TermWindow {
         let size = config.initial_size();
         let fontconfig = Rc::new(FontConfiguration::new(
             Some(config.clone()),
-            config.dpi.unwrap_or_else(|| ::window::default_dpi()) as usize,
+            self.dimensions.dpi,
         )?);
         let render_metrics = RenderMetrics::new(&fontconfig)?;
 
@@ -367,7 +367,7 @@ impl super::TermWindow {
                 + padding_top
                 + padding_bottom) as usize
                 + tab_bar_height,
-            dpi: config.dpi.unwrap_or_else(|| ::window::default_dpi()) as usize,
+            dpi: self.dimensions.dpi,
         };
 
         self.apply_scale_change(&dimensions, 1.0, window);