Write liquescent via nc@curve

[yinanazhou]

Neon issue DDMAL/Neon#1169

[yinanazhou]

Updated changes:

• Add SetLiquescent() to change note head shape
• Fix writing and reading liquescent, example:

<neume xml:id="m-354f1330-2a4b-45bc-8827-67691bd19d78">
    <nc xml:id="m-a7f25736-be07-49de-8a59-88e2341f5fb3" facs="#m-798034aa-80da-46a5-afe5-6745a0567387" oct="2" pname="d" tilt="n"/>
    <nc xml:id="m-d8b82058-2d30-4679-8b22-658f937a9888" facs="#m-aad0fb4a-8437-4d62-bdf5-523cddec911e" oct="2" pname="c" curve="a">
        <liquescent xml:id="l638nb2"/>
    </nc>
</neume>

• Fix drawing liquescent

[lpugin]

Normally we always render child elements individually. So if the encoding is:

<nc>
  <liquescent/>
</nc>

We expect the liquescent to be drawn in a call to DrawLayerChildren so the SVG will be

<g class="nc">
  <g class="liquescent"/>
</g>

This is important if you have editorial markup:

<nc>
  <add>
     <liquescent/>
   </add>
</nc>

Which then becomes:

<g class="nc">
  <g class="add">
    <g class="liquescent"/>
  <g/>
</g>

Which allows (for example) to highlight what has been added. This would be missing with your implementation because <liquescent> drawing is happening in nc drawing.

[yinanazhou]

I've added DrawLiquescent. Now the SVG for liquescent is like this:

<g id="nd7xrcn" class="neume" style="fill: rgb(221, 0, 0);">
   <g id="nj2ffc8" class="nc" stroke="black" stroke-width="30px">
      <g id="lb68cfw" class="liquescent">
         <use xlink:href="#E9BE-1dxljrq" x="841" y="487" height="223px" width="223px"></use>
         <use xlink:href="#EB98-1dxljrq" x="841" y="500" height="223px" width="223px"></use>
         <use xlink:href="#E994-1dxljrq" x="841" y="500" height="223px" width="223px"></use>
         <use xlink:href="#EB99-1dxljrq" x="841" y="500" height="223px" width="223px"></use>
         <use xlink:href="#E9BE-1dxljrq" x="872" y="480" height="223px" width="223px"></use>
      </g>
   </g>
</g>