ui.scroll-width has no effect since the floem rewrite

Lapce Version

0.4.6, built from master (c9e4c339)

System information

Windows 10 Enterprise LTSC 1809 on a touch panel; also seen on Windows 11 Pro

Describe the bug

The ui.scroll-width setting has no effect. It appears in the settings dialog with the description "Set the width for scroll bar", defaults/settings.toml gives it a value of 10, and changing it — to 60, for instance — changes nothing at all.

Additional information

The setting is never read. UIConfig provides getters for scale, font_size, font_family, header_height, icon_size, status_height and palette_width, but none for scroll_width, and the field itself is private. Every other occurrence of scroll_width in the tree is an unrelated local variable in plugin.rs.

The width is fixed in two places instead:

• paint_scroll_bar in lapce-app/src/editor/view.rs uses const BAR_WIDTH: f64 = 10.0, which positions the separator line and the git change markers
• floem's scroll handle and track keep their default Thickness of 10px, because the editor's scroll view never sets it

This is a regression. Before the floem rewrite the setting worked: lapce-ui/src/scroll.rs sized the bars from it (lines 422 and 464), and config.ui.scroll_width() existed. Both went away with 774008f5 ("remove lapce-data and lapce-ui", 10 Aug 2023) — the setting stayed behind.

That also means the resolution of #1220 ("Scroll bars too narrow") is effectively gone. On a touch screen a 10px bar is genuinely hard to hit, which is what that issue was about.

I have a fix ready and would be happy to open a PR: re-add the getter, feed it to floem's handle and track thickness as well as to paint_scroll_bar, and keep 10px as the fallback when the value is zero. Tested on a touch panel — with the setting honoured, the bar is comfortably draggable with a finger again, and the git change markers scale with it.