Rename .btn-*-outline to .btn-outline-*

[pinin]

health men, just my opinion
I think the class names for button style outline in v4, it should be following

... class="btn btn-outline-primary" ...
... class="btn btn-outline-secondary" ...
... class="btn btn-outline-success" ...
... class="btn btn-outline-warning" ...
... class="btn btn-outline-danger" ...

instead of

... class="btn btn-primary-outline" ...
... class="btn btn-secondary-outline" ...
... class="btn btn-success-outline" ...
... class="btn btn-warning-outline" ...
... class="btn btn-danger-outline" ...

that is not only a clearer, but can be used for example, another modification as

[class^='btn-outline-'],
[class*=' btn-outline-'] { ... }

which is not possible now

[cvrebert]

that is not only a clearer, but can be used for example, another modification as

[class^='btn-outline-'],
[class*=' btn-outline-'] { ... }

I believe we're trying to avoid those sorts of selectors for performance and extensibility reasons.

[mdo]

Changed in #18772.