editor: Represent scroll offset with more precision (#39367)

Closes #5355

Release Notes:

- Fixed rendering glitches with files with more than 16 million lines
(that occured due to floating number rounding errors).

---------

Co-authored-by: Smit Barmase <heysmitbarmase@gmail.com>

crates/git_ui/src/commit_modal.rs

@@ -40,7 +40,8 @@ impl ModalContainerProperties {
         let font_size = style.font_size.to_pixels(window.rem_size());
 
         if let Ok(em_width) = window.text_system().em_width(font_id, font_size) {
-            modal_width = preferred_char_width as f32 * em_width.0 + (container_padding * 2.0);
+            modal_width =
+                f32::from(preferred_char_width as f32 * em_width + px(container_padding * 2.0));
         }
 
         Self {