Prefix QGIS models with `Qgs` and qgis-js models with `Qjs`

I dislike that we exported `QgsPointXY` as `PointXY`, `QgsRectangle` as `Rectangle` etc.

I suggest to transparently export the `Qgs`-prefix to the JS/TS API and add a `Qjs`-prefix to models that only exist in qgis-js (e.g. out `MapLayer` abstraction)

@wonder-sk what do you think? I Would love to merge a PR and create a new npm version before the next workshop at FOSSGIS (27.03.)
