Support middle function of dominant-baseline for <text>

[henry-hsieh]

This PR adds supports "middle" value of dominant-baseline.

Following is the example SVG:

<?xml version='1.0' encoding='UTF-8'?>
<svg height='82' preserveAspectRatio='xMidYMid meet' xmlns:svg='http://www.w3.org/2000/svg' version='1.0' viewBox='0 0 841 82' width='841' xmlns:xlink='http://www.w3.org/1999/xlink' xmlns='http://www.w3.org/2000/svg'>

  <text dominant-baseline='middle' font-family='M+ 1p Fallback' font-size='20' text-anchor='start' x='44' y='22'>31</text>
  <text dominant-baseline='middle' font-family='M+ 1p Fallback' font-size='20' text-anchor='end' x='196' y='22'>24</text>
  <text dominant-baseline='middle' font-family='M+ 1p Fallback' font-size='20' text-anchor='start' x='204' y='22'>23</text>
  <text dominant-baseline='middle' font-family='M+ 1p Fallback' font-size='20' text-anchor='end' x='356' y='22'>16</text>
  <text dominant-baseline='middle' font-family='M+ 1p Fallback' font-size='20' text-anchor='start' x='364' y='22'>15</text>
  <text dominant-baseline='middle' font-family='M+ 1p Fallback' font-size='20' text-anchor='end' x='516' y='22'>8</text>
  <text dominant-baseline='middle' font-family='M+ 1p Fallback' font-size='20' text-anchor='start' x='524' y='22'>7</text>
  <text dominant-baseline='middle' font-family='M+ 1p Fallback' font-size='20' text-anchor='end' x='676' y='22'>0</text>

  <line stroke='#000000' stroke-width='1' x1='40' x2='200' y1='41' y2='41'/>
  <line stroke='#000000' stroke-width='1' x1='40' x2='200' y1='81' y2='81'/>
  <line stroke='#000000' stroke-width='1' x1='200' x2='200' y1='41' y2='81'/>
  <line stroke='#000000' stroke-width='1' x1='40' x2='40' y1='41' y2='81'/>

  <text dominant-baseline='middle' font-family='M+ 1p Fallback' font-size='20' text-anchor='middle' x='120' y='62'>field3</text>

  <line stroke='#000000' stroke-width='1' x1='200' x2='360' y1='41' y2='41'/>
  <line stroke='#000000' stroke-width='1' x1='200' x2='360' y1='81' y2='81'/>
  <line stroke='#000000' stroke-width='1' x1='360' x2='360' y1='41' y2='81'/>
  <line stroke='#000000' stroke-width='1' x1='200' x2='200' y1='41' y2='81'/>

  <text dominant-baseline='middle' font-family='M+ 1p Fallback' font-size='20' text-anchor='middle' x='280' y='62'>field2</text>

  <line stroke='#000000' stroke-width='1' x1='360' x2='520' y1='41' y2='41'/>
  <line stroke='#000000' stroke-width='1' x1='360' x2='520' y1='81' y2='81'/>
  <line stroke='#000000' stroke-width='1' x1='520' x2='520' y1='41' y2='81'/>
  <line stroke='#000000' stroke-width='1' x1='360' x2='360' y1='41' y2='81'/>

  <text dominant-baseline='middle' font-family='M+ 1p Fallback' font-size='20' text-anchor='middle' x='440' y='62'>field1</text>

  <line stroke='#000000' stroke-width='1' x1='520' x2='680' y1='41' y2='41'/>
  <line stroke='#000000' stroke-width='1' x1='520' x2='680' y1='81' y2='81'/>
  <line stroke='#000000' stroke-width='1' x1='680' x2='680' y1='41' y2='81'/>
  <line stroke='#000000' stroke-width='1' x1='520' x2='520' y1='41' y2='81'/>

  <text dominant-baseline='middle' font-family='M+ 1p Fallback' font-size='20' text-anchor='middle' x='600' y='62'>field0</text>
  <text dominant-baseline='middle' font-family='M+ 1p Fallback' font-size='20' text-anchor='middle' x='760' y='62'>register0</text>

</svg>

This is the render figure before the change (texts are not in the middle of the box):

This is the render figure after the change (texts are in the middle of the box):

[mogest]

Hi @henry-hsieh, thanks so much for the PR! The tests are failing due to the addition of the new property.

You might consider only adding dominant_baseline into opts if it's a non-auto value?

[henry-hsieh]

Hi @mogest, I updated the code as your request.

BTW, is there any chance for updating the version of prawn-svg after this PR merged into the master branch?

I'm using a package called bytefield-svg which is heavily using the dominant-baseline to generate svg images (just like the images I put in the PR). This package is an add-on of the Asciidoctor PDF which is using prawn-svg to render svg. I hope this update could help somebody using the same package. Thank you!

[mogest]

Thanks @henry-hsieh! I'll do a new release today.