Provide away to make URI/resource nodes from `ValueArray` strings with prefix expansion.

[skwlilac]

In trying to create an array of URI for some 'static' notes I tried the following:

r_auth_notes : "{value('sf-auth-note:').append( value([ 1,2,3,4 ]) ).asRDFNode() }"

without the trailing asRDFNote one is left with a string and for some reason elsewhere template expansion of

<core:note> : "<{r_auth_notes}>"

fails to see sf-auth-note: as a URI prefix rather than a URI scheme. .asRDFNode() will apply prefix expansion but has not been written (in ValueBase) to handle arrays.

[PR with suggested changes to follow]

[skwlilac]

In prep'ing for a PR is has become apparent that ValueBase.asRDFNode() does not apply prefixes, so it is not appropriate to make the array variant do anything different. Elsewhere I've use GlobalFunctions.asResource to make resource ValueNodes, though it is approriate to make .asRFDNode() 'work' on ValueArrays.

Instead I've added and asResource method to ValueArray although an alternate or additional approach might be to make GlobalFunctions.asResource work for Collection values as well.