Get Qt build settings from 'vcapp' qmake template

Extract all settings required to integrate Qt tools in the project build by calling qmake with the option to generate an msvc project (qmake -tp vc).

Qt/MSBuild relies on qmake to obtain settings needed to integrate Qt tools in the project build. This is currently achieved by calling qmake to generate an "empty" Makefile, which is then parsed to extract macros, include paths and aditional linker input. However, some important settings are not currently extracted, e.g. compiler and linked options.

Using an msvc project as source of the build settings, instead of a Makefile, has the advantage that all settings are already defined as MSBuild properties. As such, the extraction process will only need to append the properties in the generated .vcxproj to the ones defined in the user's project.