Add express examples for remaining express functions

[gshotwell]

How To

Check off an example when you start working on it and push directly to this branch with each update.

• Examples are in shiny/api-examples
• Examples should be named app-express.py (or app-{more-descriptive-name}-express.py)
• If no example is needed for express use @no_example("express") before (below) @add_example() to suppress errors.

  from ._docstring import add_example, no_example_express
  
  @add_example()
  @no_example("express")
  def thing_in_core():
      ...

Todo

• Remove the early exit in docs._renderer.check_if_missing_expected_example so that it will error if a function is added to the Express docs that doesn't have an example.

Remaining Apps to Translate

• accordion
• accordion_panel
• as_fillable_container
• as_fill_item
• card
• card_body
• card_footer
• card_header
• close
• data_frame
• download
• download_button
• download_link
• dynamic_route
• event
• extended_task
• file_reader
• include_css
• include_js
• insert_accordion_panel
• insert_ui
• modal
• navset_hidden
• nav_panel
• notification_show
• on_ended
• on_flush
• on_flushed
• output_image
• output_plot
• output_table
• output_text
• output_transformer
• output_ui
• page_fixed
• page_fluid
• panel_title
• poll
• popover
• remove_accordion_panel
• remove_ui
• Renderer
• req
• row
• SafeException
• send_custom_message
• showcase_bottom
• showcase_left_center
• showcase_top_right
• SilentCancelOutputException
• SilentException
• tooltip
• update_accordion
• update_accordion_panel
• update_action_button
• update_checkbox
• update_checkbox_group
• update_date
• update_date_range
• update_navs
• update_numeric
• update_popover
• update_radio_buttons
• update_select
• update_selectize
• update_sidebar
• update_slider
• update_text
• update_tooltip
• value_box