Added the ability to clone a views display while changing the display plugin

[klonos]

This is the same change as committed in Views 7.x back in May: https://www.drupal.org/node/1401778

If you have multiple displays, and one page display has overridden fields or style plugin settings, and you want to create a block display that has those exact settings, you have to manually rebuild it.

The idea is that you could choose the new display plugin while cloning, along with a warning saying that all display settings will be unconditionally thrown away. Some display plugins share similar setting names that mean different things, so there should be no attempt to translate those.

[laryn]

Great idea.

[herbdool]

Wow, so simple but works great! This could have saved me many hours over the years. Rtbc

[laryn]

Agreed -- this could save a ton of time. @klonos -- there's one fix needed in the code where a drupal_ didn't get switched to backdrop_.

[herbdool]

Good catch @laryn. I merged your change.

[philsward]

Thx for getting this going guys. It's a much welcomed addition.

[quicksketch]

Thanks folks! I merged backdrop/backdrop#3751 into 1.x and 1.20.x. Although this is a feature, we try to keep pace with core cross-ports as often as possible, so I've gone ahead and included this for 1.20.2.