Allow plugins to insert custom imports.

This patch allows a plugin to insert custom imports. These imports are
used by QtC for syntax highlighting and code completion. This way a
plugin can register types and objects that are available only at
runtime.

This is an example of an imports function implementation:

QList<Import> MyPlugin::imports(ValueOwner *valueOwner, const Document
*context) const
{
  // context is needed to know from which project is the opened document
  // in this example we don't care about multiple projects

  Import import;
  import.object = new QmlJS::ObjectValue(valueOwner, "<defaults>");
  import.valid = true;
  const ComponentVersion version(1, 0);
  import.info = ImportInfo::moduleImport("MyPlugin", version,
QString());
  auto myType = valueOwner->newObject(nullptr)
  myType->setMember("myProperty", valueOwner->valueOwner->intValue());
  // add more properties & methods/signals to myType

  import.object->setMember("MyType", myType);

  // in this example we return only one, but you care return more than
one
  return QList<Import>(import);
}

Change-Id: I395c273c7b15a9e4ed5a89a81d70ff92db2b7c0c
Reviewed-by: Marco Benelli <marco.benelli@theqtcompany.com>
Reviewed-by: Kai Koehne <kai.koehne@theqtcompany.com>

src/libs/qmljs/qmljsinterpreter.h

@@ -1124,6 +1124,15 @@ public:
     const LanguageUtils::FakeMetaMethod &fakeMetaMethod() const;
 };
 
+class QMLJS_EXPORT CustomImportsProvider : public QObject
+{
+    Q_OBJECT
+public:
+    explicit CustomImportsProvider(QObject *parent = 0) : QObject(parent) {}
+    virtual ~CustomImportsProvider() {}
+    virtual QList<Import> imports(ValueOwner *valueOwner, const Document *context) const = 0;
+};
+
 } // namespace QmlJS
 
 #endif // QMLJS_INTERPRETER_H