fix(svg-title): dont render empty title

[sudkumar]

Updates

• Don't render empty title (fixes <title> should be stripped if there is none #333)
• Preserve existing title attribute if any

Summary

Currently when no title is passed and titleProp is set to true, we are
rendering an empty title element which is causing some issues. So we
have added a conditional statement for rendering the title element only
if the title props is not falsy. If we have an existing title, that will
rendered by default. Passing the null values as the title will cause
also cause the title element for not render even if a default title
exists on the svg.

This PR also add support for preserving title attribute which may be present in the svg file.

<svg><title attr="any">Default title</title></svg>

will produce

<svg>
  {title === undefined
    ? <title attr="any">Default title</title>
    : title
      ? <title attr="any">{title}</title> 
      : null}
</svg>

Test plan

Tests have been updated.

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[codecov]

Codecov Report

Merging #341 into master will increase coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #341      +/-   ##
==========================================
+ Coverage   85.03%   85.06%   +0.03%     
==========================================
  Files          30       30              
  Lines         481      482       +1     
  Branches      134      134              
==========================================
+ Hits          409      410       +1     
  Misses         60       60              
  Partials       12       12

Impacted Files	Coverage Δ
...ckages/babel-plugin-svg-dynamic-title/src/index.js	100% <100%> (ø)	⬆️

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[gregberge]

Hello @sudkumar, looks good for me! Thanks!