This PR continues the work started in PR #8951.
This commit replaces occurences of #include "qgis.h" by #include "qgis_sip.h",
where possible = when files only depends on SIP_XXX features.
drag and drop of style .xml files to main QGIS window
Double clicking the databases or dragging them to QGIS
triggers the import from style dialog with the corresponding
input file already selected