Multiple selection dropdown menu widget for Reactive Web and Mobile

• all text is customisable
• all text is optional, except the 'This list is empty' and 'No matches found' texts
• add your own metadata to each item in the dropdown menu
  (for easy access later, without re-fetching from the database)
• option to control dropdown menu width and height
• option to display list of user selections inside the dropdown bar
• option to display count of user selections inside the dropdown bar
• option to switch from list of user selections to count of selections after n items are selected
• option to choose, per item, whether user can edit the item (i.e. select/de-select)
• option to add a 'select all' checkbox
• option to add the number of items to be selected to the label of the 'select all' checkbox
• option to add a search tool
• option to have the search tool remain visible at the top of the menu, while scrolling
• option to add a 'select all search results' checkbox
• option to add the number of items to be selected to the label of the 'select all search results' checkbox
• option to return list containing user selected items only, or return whole list
• option to keep menu open when user click away from widget
• option to keep menu open, but only when user clicks on another MultiSelect_ReactAndMob widget
• option to limit number of user selected items
• option to have dropdown menu open on load
• option to have dropdown menu "push" other content down the page when open
• option to add a clear selection icon to the dropdown bar - removes all selections

Example use case for Metadata fields:

Often the data the user makes their selection on (eg. City Names) is different to the date the app actually needs (eg. Entity Ids, Postcodes, Country).

Using the metadata fields allows you to keep the related information with the user selections so when the list of selections is returned to the parent context it does not have to perform another Aggregate etc. to get the data it actually needs.

Many thanks to @Bram Verlinden, @Nuno Rodrigues for testing and feedback, and @Soren Staun for providing feedback and suggesting the count of selected items feature!

Many thanks to @Michael111 for suggesting the user cannot edit item feature!