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/vim/src/test/neovim_backed_test_context.rs

@@ -277,7 +277,7 @@ impl NeovimBackedTestContext {
         let window = self.window;
         let margin = self
             .update_window(window, |_, window, _cx| {
-                window.viewport_size().height - line_height * visible_line_count
+                window.viewport_size().height - line_height * (visible_line_count as f32)
             })
             .unwrap();