feat(input_switch): Add .bslib-input-switch class

[gadenbuie]

• Fixes Consider putting CSS classes on input markup #740
• Adds .bslib-input-checkbox to input_checkbox() (the internal function)
• Adds .bslib-input-switch (without the above class) to input_switch()

input_checkbox("ID", "LABEL") |> print(browse = FALSE)
#> <div class="form-group shiny-input-container">
#>   <div class="bslib-input-checkbox form-check">
#>     <input id="ID" class="form-check-input" type="checkbox" role="switch"/>
#>     <label class="form-check-label" for="ID">
#>       <span>LABEL</span>
#>     </label>
#>   </div>
#> </div>

input_switch("ID", "LABEL") |> print(browse = FALSE)
#> <div class="container-fluid">
#>   <div class="form-group shiny-input-container" data-require-bs-version="5" data-require-bs-caller="input_switch()">
#>     <div class="bslib-input-switch form-switch form-check">
#>       <input id="ID" class="form-check-input" type="checkbox" role="switch"/>
#>       <label class="form-check-label" for="ID">
#>         <span>LABEL</span>
#>       </label>
#>     </div>
#>   </div>
#> </div>