Improve qdc OAI-PHM crosswalk for OCLC DCG harvest

The OCLC DCG can use the qdc OAI-PMH crosswalk for mapping items to OCLC. These fields, such as dcterms.available and dcterms.dateAccepted, with only two "segments," have the advantage of retaining their full field names. This is in contrast to dc.contributor.department and dc.contributor.committeemember, which both appear in DCG as dc:contributor:number.

Also see if we can map the thumbnail URL to a qdc field like we did for dplava. We always want the first thumbnail.

<!-- if the item is "THUMBNAIL", then take the URL value of it !!!not sure if this work because the thumbnail URL appears before the "THUMBNAIL"-->
            <xsl:for-each select="doc:metadata/doc:element[@name='bundles']/doc:element[@name='bundle']/doc:element[@name='bitstreams']/doc:element[@name='bitstream']">
                <xsl:if test="../../doc:field[@name='name']/text() = 'THUMBNAIL'">
            <edm:preview>
                <xsl:value-of select="doc:field[@name='url']/text()"></xsl:value-of>
            </edm:preview>
                </xsl:if>
            </xsl:for-each>

e.g., https://vtechworks.lib.vt.edu/oai/request?verb=GetRecord&metadataPrefix=dplava&identifier=oai:vtechworks.lib.vt.edu/oai:10919/99452

<edm:preview>https://vtechworks.lib.vt.edu/bitstream/10919/99452/5/s41598-020-60316-8.pdf.jpg</edm:preview>

Can we leave the field with that name or do we need to give it a dcterms name. Can we have custom dcterms names?

VTUL / vtechworks

Improve qdc OAI-PHM crosswalk for OCLC DCG harvest #713