Give TextEdit a min_size and a gap, via a shared LayoutStyle

`ButtonStyle` carried a `min_size` and a gap; `TextEditStyle` carried
neither, so a themed text edit could set its padding but not its height or
the gap to its prefix — the height had to travel separately on the widget,
and the gap fell back to the ambient `spacing.icon_spacing`.

A theme decides the two together, so they move into a `LayoutStyle` that
both styles embed. `TextEdit` now honors both, with defaults that keep
today's rendering: no floor of egui's own, and the gap `AtomLayout` was
already falling back to.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

crates/egui/src/theme/default_style.rs

@@ -156,6 +156,10 @@ impl StyleProvider<TextEditStyle> for DefaultStyle {
                     outer_margin: Margin::same(-(widget_visuals.expansion as i8)),
                     ..Default::default()
                 },
+                // A text edit sizes itself from the rows it holds; egui's own theme adds no floor
+                // of its own.
+                min_size: Vec2::ZERO,
+                gap: style.spacing.icon_spacing,
                 text_style: text,
                 ..Default::default()
             },

crates/egui/src/widgets/text_edit/builder.rs

@@ -494,12 +494,18 @@ impl TextEdit<'_> {
             atom_layout:
                 AtomLayoutStyle {
                     frame: styled_frame,
+                    min_size: style_min_size,
+                    gap,
                     text_style: text_visuals,
                     ..
                 },
             hint_text_color,
         } = ui.widget_style(id, &classes);
 
+        // The theme sets a floor on the size; the builder's own `min_size` can only raise it,
+        // the same way it does for a button.
+        let min_size = min_size.max(style_min_size);
+
         let text_color = text_color
             .or_else(|| ui.visuals().override_text_color)
             .unwrap_or(text_visuals.color);
@@ -743,6 +749,7 @@ impl TextEdit<'_> {
 
             let allocated = AtomLayout::new(atoms)
                 .id(id)
+                .fallback_gap(gap)
                 .min_size(Vec2::new(allocate_width, min_height.at_least(min_size.y)))
                 .max_width(allocate_width)
                 .sense(sense)