Import primer-dropdown from github

[jonrohan]

closes #338

This PR imports primer-dropdown as a new component. And refactors it to use our spacing scale as well as cleans up some class names.

TODO

• Add primer-dropdown as a dependency of primer-product
• Add @import "primer-dropdown/index.scss"; to primer-product/index.scss
• Address Mu-An's feedback in Import primer-dropdown from github #393 (comment)
• Update the base to the next release branch (10.11.0?)

[dmalan]

Hi all, just wanted to ask if there are (short-term) plans to merge dropdowns into master? (I see that they're listed as stable in https://styleguide.github.com/primer/components/dropdown/ but I gather that might be from when they were a separate repo?)

And if/when they are merged in, will Primer include the requisite JavaScript or would users of the library need to handle toggling?

Thanks!

[shawnbot]

I'm queueing this up for #531. @jonrohan, do you mind fixing up the version conflicts and taking a look at the comments above? 🙇

[muan]

I wasn't sure if it made sense to keep the js-bulk-actions, and js-transitionable classes in the log out menu example. I think the js-menu-close classes can go since I've killed off the js-menu-container though, right? I'm thinking that for the purposes of the style guide it might make sense to remove all of the js- classes since they aren't going to work in the style guide anyway. What do you think?

Yup! js-bulk-actions, js-transitionable should go since they have ~0 to do with the menu functionality.

However, on <details> the js-menu-close behavior is now either handled by <details-menu> or done throughdata-toggle-for="explict-id-on-details-tag". Given this..... I am changing my mind regarding whether to include <details-menu>. I think we should 🤔 , at least for one example.

I see style guide as a place people can find a fully functioning + clean code snippet that they would just edit and go. Copy/pasting from the codebase are likely to result in a lot of unnecessary markup/js/css class duplication. And in this case, without details-menu it's kinda of not fully functioning.

What do you think?

[shawnbot]

@muan thanks, I think that makes a ton of sense. I just need to get the custom element bundles into ours before I can make that work.

[shawnbot]

@jonrohan I'm inclined to file an issue for updating the docs so that we can get this out in #588. What do you think?

[shawnbot]

These styles are in the process of being refactored in dot-com, so I'm going to open a new PR with some fresh CSS when it's ready to bring into the fold. Thanks for your feedback, @muan!