Improvements on QMLTC file generation: uppercase and more explanatory filename

Reproducer attached. Go to "Preferences->C++->File Naming" and uncheck "Lower case file names", and build the reproducer. But still, within <build_dir>/.qmltc/<target_name>, all generated files are lower case.

Update: this is not necessarily about "uppercase" vs "lowercase" anymore. In a nutshell, the generated filename should follow the QML file name, irrespective of case.