[Feature Request] add size attribute to dcc.Dropdown

[geomatix-au]

Hey guy, was wondering if you could add the size attribute to the dcc.Dropdown so that we have the ability to show all the select options rather than display a vertical scrollbar if you have more than 6 options.

In a normal html select tag you can specify a size attribute as follows:

See https://developer.mozilla.org/en-US/docs/Web/HTML/Element/select for more info about the size attribute.

[alexcjohnson]

Closed by @AnnMarieW in #2109 by adding a maxHeight prop 🎉