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/gpui/examples/data_table.rs

@@ -402,7 +402,7 @@ impl Render for DataTable {
                     .overflow_hidden()
                     .border_1()
                     .border_color(rgb(0xE0E0E0))
-                    .rounded_md()
+                    .rounded_sm()
                     .child(
                         div()
                             .flex()

crates/gpui/examples/window.rs

@@ -16,7 +16,7 @@ fn button(text: &str, on_click: impl Fn(&mut Window, &mut App) + 'static) -> imp
         .active(|this| this.opacity(0.85))
         .border_1()
         .border_color(rgb(0xe0e0e0))
-        .rounded_md()
+        .rounded_sm()
         .cursor_pointer()
         .child(text.to_string())
         .on_click(move |_, window, cx| on_click(window, cx))