feat(moveElemsAttrsToGroup): improve attribute flow

[KTibow]

Sometimes there is a svg or a g that has a redundant attribute, like this:

<svg fill="red">
    <rect fill="blue"/>
    <circle fill="blue"/>
</svg>

These can be removed.
And sometimes the defaults are inefficient, like this:

<svg>
    <g fill="red">
        <path/>
        <rect fill="blue"/>
        <circle fill="blue"/>
    </g>
</svg>

The default can be changed to something more efficient. This PR does that.

* This would be even better if it moved attributes from/to svg, but I'm not sure if I should implement that.
* If the default-changing is too much, I'm fine removing everything except for the redundant attribute remover.

Results

Join this with #1894 for better performance on icon sets. On Isometric Madness compared to current SVGO, this does -3221 bytes without multipass and -4343 with.