GROOVY-6621 fix Node#text when value is NodeList

by accounting for non-String children elements
existing difference from o.w.d.Document
Merge branch 'master' into GROOVY-6621-Node-text-when-NodeList-value
in preparation for moving the original tests
move NodeTests to main project
update for changes to text() method
Merge branch 'master' into GROOVY-6621-Node-text-when-NodeList-value
minor refactor
minor refactor
Merge pull request #364 from ml10/GROOVY-6621-Node-text-when-NodeList-value

GROOVY-6621 fix Node#text when value is NodeList
minor test refactor - remove dependency on XmlParser used to create test node tree
GROOVY-6672: ClassFormatError if trait (accidentally) "extends" interface
GROOVY-6670: Reorder searches for class nodes in closure signature hint
GROOVY-6621: groovy.util.Node#text incorrect when value is a NodeList (additional test to capture current behavior for getting local text)
GROOVY-6676: The type checker doesn't use the right receiver type to perform return type inference
GDK / GroovyDoc restyling: additional tweaks so both documentations are coherent style-wise
Merge pull request #372 from glaforge/gdk-groovydoc-tweaks

GDK / GroovyDoc restyling: additional tweaks so both documentations more coherent style-wise