ScrollArea improvements for user configurability (#5443)

* Closes <https://github.com/emilk/egui/issues/5406>
* [x] I have followed the instructions in the PR template

The changes follow what is described in the issue with a couple changes:
- Scroll bars are not hidden when dragging is disabled, for that
`ScrollArea::scroll_bar_visibility()` has to be used, this is as not to
limit the user configurability by imposing a specific function. The user
might want to retain the scrollbars visibility to show the current
position.
- The input for mouse wheel scrolling is unchanged. When I inspected the
code initially I made a mistake in recognizing the source of scrolling.
Current implementation is in fact using
`InputState::smooth_scroll_delta` and not `PassState::scroll_delta`,
therefore it is possible to prevent scrolling by setting the
`InputState::smooth_scroll_delta` to zero before painting the
`ScrollArea`.

A simple demo is available at
https://github.com/MStarha/egui_scroll_area_test

crates/egui_extras/src/table.rs

@@ -4,7 +4,7 @@
 //! Takes all available height, so if you want something below the table, put it in a strip.
 
 use egui::{
-    scroll_area::{ScrollAreaOutput, ScrollBarVisibility},
+    scroll_area::{ScrollAreaOutput, ScrollBarVisibility, ScrollSource},
     Align, Id, NumExt as _, Rangef, Rect, Response, ScrollArea, Ui, Vec2, Vec2b,
 };
 
@@ -745,7 +745,10 @@ impl Table<'_> {
 
         let mut scroll_area = ScrollArea::new([false, vscroll])
             .id_salt(state_id.with("__scroll_area"))
-            .drag_to_scroll(drag_to_scroll)
+            .scroll_source(ScrollSource {
+                drag: drag_to_scroll,
+                ..Default::default()
+            })
             .stick_to_bottom(stick_to_bottom)
             .min_scrolled_height(min_scrolled_height)
             .max_height(max_scroll_height)