Converter::Map only maps first of sibling elements

[scpeters-test]

Original report (archived issue) by Steve Peters (Bitbucket: Steven Peters).

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The Converter::Map functionality was added to libsdformat9 in pull request #580. It maps values from elements/attributes into other elements/attributes. It is currently limited to only mapping the first of sibling elements of the same type.

For example, consider the following xml from a .convert file:

<map>
  <from name='elemD'>
    <value>d</value>
    <value>D</value>
  </from>
  <to name='elemF'>
    <value>f</value>
    <value>F</value>
  </to>
</map>

that operates on the following xml:

<elemC attrC='C'>
  <elemD>D</elemD>
  <elemD>D</elemD>
  <elemD>d</elemD>
  <elemD>d</elemD>
</elemC>

Currently it only maps the first element, so the output would be the following (all the original elemD elements plus one new elemF element):

<elemC attrC='C'>
  <elemD>D</elemD>
  <elemD>D</elemD>
  <elemD>d</elemD>
  <elemD>d</elemD>
  <elemF>F</elemF>
</elemC>

I've added a failing test to the following branch that expects all sibling elements to be mapped in the converted xml:

• https://scpeters-test.github.io/gh-pages_sdformat_fast_export/#!/osrf/sdformat/branch/converter_map_multiple_siblings