gpui: Rename rounded_md to rounded_sm (#26228)

This PR renames the `rounded_md` style method to `rounded_sm`.

Follow up to https://github.com/zed-industries/zed/pull/26221, which
freed up the `rounded_sm` name.

Release Notes:

- N/A

crates/markdown/src/markdown.rs

@@ -690,7 +690,7 @@ impl Element for MarkdownElement {
                                     .flex()
                                     .border_1()
                                     .border_color(cx.theme().colors().border)
-                                    .rounded_md()
+                                    .rounded_sm()
                                     .when(self.style.table_overflow_x_scroll, |mut table| {
                                         table.style().restrict_scroll_to_axis = Some(true);
                                         table.overflow_x_scroll()