Rename close icon class to btn-close

Imo:

1. close name is very generic, but adds a lot of styling and interferes with any use of such word for other purposes. Example: For buttons with icons I often use btn btn-secondary <icon-name>, If my icon is named close the button will get a lot of unwanted styles.
2. Close icon’s use-case is generally a button, so why not btn btn-close?

[MartijnCuppens]

What do you guys think about a more generic name, something we could apply for more buttons which have icons like the navbar toggler button?

[calvinkarpenko]

I think it would be worthwhile to make it in line with other “buttons”, for the sake of consistency. It would break things, but that’s the reason breaking changes are made on major versions. It’ll be changed in the documentation as well and anyboody updating to version 5 will, upon finding the close button not working, no dobut check the documentation and realise it has been changed, or will check a changelog.