Add 312-bslib-sidebar-resize

[gadenbuie]

Adds a manual testing app for plot and output resizing in sidebars (without cards).

Pairs with rstudio/bslib#566 where this behavior is improved for sidebars.

Expected behavior

In the app below, both the "static" ggplot2 output and the htmlwidget plotly plot output will stretch during the sidebar transition. The static plot will re-render when the transition is complete, so there's a small "snap" when the new plot is rendered. (No snap is seen in the case of an htmlwidget like plotly.)

All plots stretch during resize when the shared sidebar is toggled; only the sidebar in the local sidebar layout stretches when the local sidebar is toggled.

Kapture.2023-05-09.at.15.56.42.mp4

Failing behavior

When the behavior isn't present, neither the plot nor the htmlwidget's will update its width until after receiving a re-render event from the server.

Kapture.2023-05-09.at.15.55.44.mp4

[schloerke]

I'm happy that it is automated. I'll let you and @cpsievert work out the details

[cpsievert]

@gadenbuie do you know why these tests fail pretty consistently on Windows (and sometimes on Mac)?

[gadenbuie]

The Mac 3.6.3 errors are due to ggiraph

  Error: Error: package or namespace load failed for ‘ggiraph’:
   object 'guide_gengrob' not found whilst loading namespace 'ggiraph'
  Error: Error: loading failed
  Execution halted
  ERROR: loading failed

I was just starting to try to figure out how to look into the Windows failures (any ideas?)

[gadenbuie]

There's some general flakiness in this PR that I want to resolve before merging. Carson and I talked through some options in person, one of which would be to do all of the sidebar size polling in the browser, rather than communicating back and forth via shinytest2.