QQmlJSImporter: Do not mix up cpp and qml names

QQmlJSScope::findType() is used in qqmljsimportvisitor and qqmljsimporter with a contextualtypes. Contextualtypes is a map from string to qml and cpp names, which makes the code pretty confusing to read as one never knows if the current name is a qml type or a cpp type.

Tasks:

• find out why qqmljsimporter mixes up composite and non-composite types
• if it has a good reason: document this strange behavior with internal documentation everywhere it happens
• Otherwise: refactor ContextualTypes and QQmlJSImporter to separate composite and non-composite types