Improve QML library

[acolombier]

Depends on #16658

Refactor the QML library to reduce the node count and reduce the strain on the data model. Also leverage some of the Qt 6.5+ and 6.8+ TableView improvement to provide a full table customisation experience (column resizing, moving, filtering,...)

This is providing a net performance improvement!

@xARSENICx I have reverted 881d9d7 as it made the devx absolutely dreadful: any invalid work in progress would lead to Mixxx stopping, forcing the restart the debug session every time. What was the reason for making this change? Arguably, we could guard it being the --developer flag?

[xARSENICx]

Long term, LateNightQML should move out from behind --developer. But today it is still experimental, and this commit fixes real QML startup/development issues we still need while getting there. So I’d rather not revert it.

The better intermediate step is to guard the special profile-risk bypass behind the --developer flag, while keeping the QML load-failure and qt compatibility fixes.

CC @JoergAtGithub

[JoergAtGithub]

@xARSENICx it seems you mixed the commits here. 881d9d7 is the commit that ensure that the QML testcases work. And that changes on new-ui do not break LateNightQML and vice versa. It prevents also annoying case that a user double clicks on Mixxx and nothing happens because main.qml could not load and generate alien processes which can only killed by task manager.

[JoergAtGithub]

Please restore that the behavior that Mixxx fails, if QML is not loadable. You might bypass it by a combination like --new-ui and --developer, but for normal users and the unit tests it must fail reliable.

[acolombier]

The QML interface is highly unstable and this kind of early changes prevent fast prototyping. I have reworked it so the behaviour continue allowing failure if if --developer is passed.

881d9d7 is the commit that ensure that the QML testcases work. And that changes on new-ui do not break LateNightQML and vice versa

Could you please clarify how is this test useful for unit test? I understand that having loadQml returning a value allow asserting, but surely exit(-1) is not needed to pass unit tests?