Condense the dropup example

data-example-id not need be moved. Only change, because data-example-id="static-dropdown" already exists.

Remove whitespace after h3.
Variation not need capitalize.

* Remove `<h3>Example</h3>;`
* Move `data-example-id=""` to `<h3>Dropup Variation</h3>` and change value;

Fix issue #15597 — Mention dropup variation in dropdown docs

Other pull request was so messed up I sincerely have no clue how to save it. The recommended command doesn't work, can't believe rebasing is so problematic...

Removed "Separated link" in example where it's not separated. This may confuse people to think that it is separated.

I don't want to sound nitpick, but I've been working with a client maintaining a custom internal Bootstrap installation with customized docs, so I've been getting a lot of feedback from client developers using the docs.

Refs #11410

[skip sauce]

Closes #14951 by merging it.

possibly less confusing option, as per discussion, is to always show the
dropdown trigger button (both live and in that code example)

Assuming sr-only is used in the actual live code so that the menu can be
shown open already ... but having sr-only in the highlighted example
code itself is confusing/misleading.

Also, change the text for the button from "Dropdown" to "Dropdown
trigger" for clarity (and it then matches
http://getbootstrap.com/javascript/#dropdowns)