Adjust feedback icon position and padding for select.form-control

[mdo]

Fixes #31219.

Doesn't add any new variables for now, instead doing the operations inline. Unsure if it's worth really adding a variable for this anyway, but if so, we can do it in a v4.7.x release.

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[XhmikosR]

If we backport #33131 I think we can make the next release a 4.7.0 release? So, I'd say you could add a new variable otherwise better add a TODO so that we don't forget about it.