Use std::unordered_map for m_storageIndices
Use std::unordered_map for m_storageIndices

Makes the Ir event count go from ~8.28 billion to ~8.12 for a
Qt Creator null build.

Change-Id: I02714cd922fd9d42abe67e5115e3ffd64778f77a
Reviewed-by: Christian Kandeler <3aa99dcdd3f0cac61fb81c2a11771c0cc2497607@qt.io>

qt-labs/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qt-labs/qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs,qt-labs/qbs,qtproject/qt-labs-qbs,qtproject/qt-labs-qbs