[v1] Adapt for input group changes

[Herst]

Thinking aloud

• E006 (.input-group contains a <select>/<textarea>) ➜ Works now with <select>/<textarea> with the .form-control/.custom-select classes respectively (https://getbootstrap.com/docs/4.1/components/input-group/#custom-select/https://getbootstrap.com/docs/4.1/components/input-group/#basic-example) ➜ Replace with new checks in future ([v1] (Possible) checks to be added #424) but remove for now
• E009 (Button and input sizing within .input-groups can cause issues.) ➜ Still applies? ➜ Change .input-lg into .form-control-lg
• E010 (Input groups cannot contain multiple .form-controls) ➜ Works at least with multiple <input>s except for validation (https://getbootstrap.com/docs/4.1/components/input-group/#multiple-inputs) ➜ Warning? Remove for now.
• E011 (.input-groupand.form-groupcannot be used directly on the same element) ➜ Still applies I guess ➜ Port by addingrow/.form-row`
• E012 (.input-groupand.col--` cannot be used directly on the same element) ➜ Port
• E015 (Multiple add-ons on a single side of an input group not allowed) ➜ Works now (https://getbootstrap.com/docs/4.1/components/input-group/#multiple-addons) ➜ Remove check
• E044

Changes

E006, E010, E015 removed and E009, E011, E012, E044 ported

Status

• Code: Done
• Tests: Done
• Wiki: Done

[Herst]

Apparently the changes to the tests got lost, redoing them.

[XhmikosR]

From a quick look it's looks OK. I don't have the time to properly review this, though.