fix(306,308,310): Sidebar and accordion updates

[gadenbuie]

Minimizes transitions in sidebar by setting

.bslib-sidebar-layout {
  --bslib-sidebar-transition-duration: 5ms;
};

It turns out we need a little transition time or the final part of the sidebar state transition lifecycle doesn't happen.

TODO

• 308-sidebar-kitchen-sink
• 310-bslib-sidebar-dynamic
• 308-sidebar-kitchen-sink top padding on mobile
• Can the changes in this PR also fix 306

[gadenbuie]

This will still exhibit failures for the following reasons.

✅ 310-bslib-sidebar-dynamic

Nested sidebars on mobile don't account for the taller space requirements of the toggle.

• Inline padding of sidebar main area on mobile screens with nested sidebars bslib#859

✅ 308-sidebar-kitchen-sink

The flakiness in this test seems to be a problem with how chromote/Chrome take screenshots. Here's a screen recording of the screenshot process for the first tab, slowed down to 1/16 speed. You can clearly see some re-layout happens and it's very likely the screenshot happens just before the layout settles.

shinytest2-screenshot-reload-slow.mov

It looks like shinytest2 defaults to delay = 0, whereas chromote's screenshot() method uses delay = 0.5. I upped the delay in 308 to 0.25 with

AppDriver$new(
  variant = platform_variant(),
  name = "308-sidebar-kitchen-sink",
  # ...
  # Set a delay to screenshot after layout is settled
  screenshot_args = list(delay = 0.25)
)

[gadenbuie]

I finally figured out 308 -- I disabled the sidebar transition during the portion of the tests where we need to screenshot the closed sidebar. Then we re-enable the transition by removing the CSS that disabled it, before toggling the sidebar and screenshotting it in the open state.

[gadenbuie]

@cpsievert I've fixed the sidebar position, but it looks like theres a bug here that could be 1) a selectize issue; 2) an accordion issue; or 3) a bug in the test app. I poked at it a bit but didn't find an easy answer. (Note I also tried with the latest selectize fixes in shiny PR 3923.)