Label objects would produce invalid SVG XML, because the stroke-linecap
property was added as if it was a style (with : and ;), but it was
inserted in the XML tag directly, rather than inside the style attribute
value. The invalid SVG prevented for example a TechDraw draft view from
rendering when it contained a label.
This was added in commit 6a7912d399 (Draft: Using square endcaps for
lines in SVG output).
This stroke-linecap is supported both as a presentation attribute inside
the style or a XML attribute, so for consistency with the surrounding
attributes, it is made a normal attribute, rather than putting it inside
the style.
See also https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/stroke-linecap
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