Fix text rotation

[tikitu]

This PR does two things:

• adjusts the SPM package to allow the tests to run under SPM (the change introduces no new failures), and
• fixes a bug in how rotated text renders in SwiftUI.

Text rotations weren't being applied to the SwiftUI view in quite the same way as in the SVG renderer (the transformation wasn't using the same origin coordinates).

Take the small example SVG:

<svg xmlns="http://www.w3.org/2000/svg"
xmlns:xlink="http://www.w3.org/1999/xlink" version="1.1" class="marks"
width="100" height="100" viewBox="0 0 100 100">
<g transform="translate(10,10)">
<rect width="65" height="65" fill="pink"/>
<text text-anchor="start" transform="translate(2,6) rotate(45)" font-family="sans-serif"
font-size="10px" fill="#000" opacity="1">AAAAAAAAAAAA</text>
</g>
</svg>

SVGView before this fix	Rendered in your browser	Screenshot from SVG viewer Gapplin	SVGView after this fix