Feature/textpath path 417

[ljluestc]

Closes #417

Description

Implements support for the path attribute of the SVG <textPath> element, as specified in SVG2 TextPathElementPathAttribute. This allows <textPath> to define a path directly (e.g., path="M10,20 L100,100") instead of requiring an xlink:href to a <path> element.

Changes

• Added path: Option<PathData> field to usvg::TextPath in crates/usvg/src/text.rs.
• Updated TextPath::from_xml to parse the path attribute using parser.parse_path_data.
• Modified process_text to use the path attribute’s PathData if present, falling back to xlink:href.
• Ensured parse_path_data in crates/usvg/src/path.rs converts the path attribute string to PathData.

Testing

• Manually tested with test_textpath.svg:

  <svg xmlns="http://www.w3.org/2000/svg" width="600" height="200">
      <text font-size="24" fill="blue">
          <textPath path="M10,100 Q50,50 100,100" startOffset="0">Text on Path</textPath>
      </text>
      <text font-size="24" fill="red" y="150">
          <textPath xlink:href="#path1" startOffset="0">Text on Ref Path</textPath>
      </text>
      <path id="path1" d="M10,150 Q50,100 100,150" fill="none" stroke="black"/>
  </svg>

[RazrFalcon]

That's a very strange patch. All you have to do is modify the parser to handle inline paths and not just xlink:href. But you do way too many other things.