Centralize architecture canonicalization data

The mappings of canonical architecture names to synonyms are currently stored inline in the QBS module's validate function, and the qbs-detect-toolchains' Probe class.

The data referenced by these two areas should be stored in a (JSON?) file in the share/ directory, and read when needed. This will ensure the two mappings do not diverge. Maybe later. First we need to set up a place to put data of this sort and access it easily from both C++ and QML.