Remove or adjust ionRangeSlider CSS dependency

[gadenbuie]

From https://github.com/posit-dev/py-shinyswatch/tree/e6f097b792bbba61fc4c03b0bbc78e4ae422f0c1/shinyswatch/bsw5/cerulean , shinyswatch is only aware of the ionRangeSlider and is missing selectize and datepicker. (The bootstrap.min.css is equivalent to the shiny.min.css.)

May I request a PR to add those two files (to here)? Thank you!

Originally posted by @schloerke in posit-dev/py-shiny#1191 (comment)

Ideally, after the changes in posit-dev/py-shiny#1191, theme extension packages like shinyswatch should not need to compile component dependencies. Our goal is that these would be written to target Bootstrap 5 and make use of CSS variables such that changing out the core Bootstrap CSS is sufficient.