QML compiling or linting: add more log levels for warnings/errors

For application developer, using the output of the compiler/linter on large QML bases is a valuable tool to find possible coding errors. But in fact, the output of the compiler also contains messages for correct QML code that are not fixable by the end user: they are part of Qt itself or are limitations in Qml that lead to it. Or warnings issued by the compiler that something is not yet implemented / not efficient /etc.

The way these are implemented now, is good for the scope of the "compiler developer", but tricky for the end user who wants to use the tool to find real life problems with it. Large projects can have thousands of lines of output, where most of them deal about "can be shadowed" or hard to understand messages like "Cannot generate efficient code for incomparable types QVariant of Icon::model with type QVariant and QVariant of Icon::model with type QVariant". Or dozens of messages related to QTBUG-123917 .

This renders the "Problems" tab of Qt Creator pretty useless. It's completely spammed and you don't see real problems. There was an attempt to address this with QTBUG-108757, but the solution there  was to disable all the messages, and adding a "--verbose" flag to restore the old behavior. So in the end that does not solve the request of having helpful messages to find potential issues there.

This issue could  be solved by introducing some more log levels so that a majority of these can be filtered away, but the helpful messages for the end user would be in the output.