Offset: Increase search depth when finding the 'real' offset parent

[Minimaximize]

Summary

Continue searching for the next positioned offsetParent (or the document) when calculating position().

This fixes the seemingly inconsistent behaviour that occurred when calling position() on elements inside tables; for which the offsetParent changes based on its position css property. e.g

<div id="positioned-container" style="position: relative;">
    <table>
        <tr>
            <td>
                <span id="static"></span>
                <span id="relative" style="position: relative;"></span>
                <span id="absolute" style="position: absolute;"></span>
            </td>
        </tr>
    </table>
</div>

The offsetParent of #static is td
The offsetParent of #relative and #absolute is #positioned-container

Previously $('#static').position() was returning the position relative to the containing <td> element, while $('#relative').position() was returning the position relative to #positioned-container

Now, both elements return their position relative to the containing #positioned-container

Checklist

• All authors have signed the CLA at https://cla.js.foundation/jquery/jquery
• New tests have been added to show the fix or feature works
• Grunt build and unit tests pass locally with these changes
• If needed, a docs issue/PR was created at https://github.com/jquery/api.jquery.com

[Minimaximize]

Whoops, I thought I had fixed that failing test 😓😓

[Minimaximize]

Finally tracked down the docs describing why the licence check was indeterminate - Fixed the erroneous author attributions for my commits

[mgol]

Closing & re-opening the PR to trigger the EasyCLA check...

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: Minimaximize / name: Liam James (7885262, 522b92c, 3dd9126)

[gibson042]

Thanks, this is good!

[gibson042]

While we're here making changes, we could also account for scrolling.

-				// Incorporate borders into its offset, since they are outside its content origin
+				// The origin against which we will be returning a relative position is the absolute offset
+				// of offsetParent, plus the top/left width of its borders (since they are outside offsetParent's
+				// content origin), minus its top/left scroll position (which has already affected element
+				// absolute offset and should not be counted twice)
 				parentOffset = jQuery( offsetParent ).offset();
-				parentOffset.top += jQuery.css( offsetParent, "borderTopWidth", true );
-				parentOffset.left += jQuery.css( offsetParent, "borderLeftWidth", true );
+				parentOffset.top += jQuery.css( offsetParent, "borderTopWidth", true ) - offsetParent.scrollTop;
+				parentOffset.left += jQuery.css( offsetParent, "borderLeftWidth", true ) - offsetParent.scrollLeft;

[mgol]

I guess we should add some tests for this part of the behavior then as well.

[mgol]

Extracted to #5468. @gibson042 if you have nothing against, I'd merge this PR as-is and track the remaining changes via #5468. Let me know what you think.

[mgol]

Followup work extracted to #5468 per the last team meeting.