[Fix Issue #15683] `readonly` input should not have a `not-allowed` cursor. Instead, this pull request displays a standard cursor and only displays the not-allowed cursor on disabled items.

Revise docs wording to clarify cursor display

Refs #15340

Refs #11266, #13098, #15415

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Per https://github.com/twbs/bootstrap/issues/1969#issuecomment-36971094

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- Rather than override and hack for IE8-10 and then IE11, scope to just Safari.
- Drops the IE hacks for a media query Webkit hack

Fixes #14234: Reset the hack IE8-10 with another hack just for IE11 for temporal inputs and line-height

Also, makes little sense to say that Firefox sets a `-webkit`-prefixed value

Fixes #13548: Use position: absolute; to fix checkbox and radio line-height problems that were introduced after #13003

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Per:
* http://jsbin.com/purer/2/edit
* https://github.com/cvrebert/bs-css-hacks/blob/6e8aa78384a005b007fc45327c9516dcf6ec0f30/README.md#ios-temporal-input-line-height
Thanks @mdo <3

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Fixes #13066: Add z-index to the form control feedback icons so input groups don't render on top of them

Fixes #13098
Closes #13099

Fixes #13003: Move padding on radio and checkbox options from the surrounding div to the label to remove the no-click deadzone caused by negative margin