Huge memory usage after loading MIME database

In our app (VLC) among the first things we do when loading Qt is setting the app icon. On some Windows machines (not all) loading an icon results in 460 Mo of memory being added to the app.

After some investigation I found that that he MIME type database is loaded (even though it's not used in the end). This is what loads this huge amount of memory. Specifically when parsing the content of `mimetypes\mime\packages\freedesktop.org.xml`. I did not understand how or where this memory is allocated during the QMimeTypeParserBase::parse() call but it happens in there. There are 768 mime types loaded and after that parsing is done, 460 Mo of memory are added to the app.

We did not have this issue until we switched the code from Qt 5.6 to 5.11.