FEATURE: references and backReferences FlowQuery operations

[bwaidelich]

usage

# get first reference instance
${q(node).references().get(0)}

# get first reference name
${q(node).references().get(0).name}

# get property of the first reference itself
${q(node).references("someReferenceName").referenceProperty("someReferenceProperty")}

# get property of first referenced node
${q(node).references().nodes().property("someNodeProperty")}

# the same API for back references
${q(node).backReferences("someReferenceName").referenceProperty("someReferenceProperty")}

Resolves: #4144

[bwaidelich]

TODO

• dedicated referenceProperty operation (revert property operation changes)
• new nodes operation

[skurfuerst]

@bwaidelich don't we still need the nodes() FlowQuery operation? otherwise looks good :)

[bwaidelich]

@skurfuerst doh, you're right. I'll take care!