This is more representative of what actually occurs, as web does support remote URLs which wouldn't need a romfs callback. This paves for easy future support of this with a call like 'OpenPageRemote' or similar.

This is a function that definitely doesn't always have a non-modifying
behavior across all implementations, so this should be made non-const.

This gets rid of the need to mark data members as mutable to work around
the fact mutating data members needs to occur.

These currently aren't used by anything other than the QtWebBrowser
class itself, and can be made private.

Using a custom reimplementation of QWebEngineView and an injector script.