XWIKI-18046: Layout issues on Administration's Rights section (#2985)

* Unset the vertical align of radio buttons to pick user/group that caused a weird display due to an unexpected collision
* Limited the size of the first column of the table when there's not many rights along it
* Removed auto wrapping on some elements where it created inconsistencies in UI (still looks good without it)
* Overrode an unexpected collision between xform and the rights table (only for extension rights)
* Moved the line for the unregistered user rights to be just above the actual table lines (looks more consistent than regular line (almost) -> filter -> regular line)
* Tweaked colspans on filter elements to have them display side to side using the whole length of the table
* Added comment to explain empirical value
* Added xml escaping on the $clsname use

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Co-authored-by: Manuel Leduc <manuel.leduc@xwiki.com>