YAML filter: multi-line '|' values should be produced as a single segment

Simple example attached.

The | operator (optionally with chomping terminator, |-) allows you to have multiple lines of text in a single value:

long_line: |-
    This is a
    very long line.

Currently, the behavior of the filter is to produce these as multiple trans-units within a single group:

<group id="sg1">
<trans-unit id="tu1" resname="long_line" xml:space="preserve">
<source xml:lang="en">This is a </source>
<target xml:lang="fr">This is a </target>
</trans-unit>
<trans-unit id="tu2" resname="long_line" xml:space="preserve">
<source xml:lang="en">very long line.</source>
<target xml:lang="fr">very long line.</target>
</trans-unit>
</group>

The problem with this is twofold: we split the value into multiple pieces for translation, and we have multiple TUs with a single resname.

Since these lines reflect a single value, better behavior would be to extract them as a single trans-unit.