Fix corrupted "add torrent" layout

[drew2a]

Fixes #7965

The bug is a combination of two facts:

1. QT dependencies upgrade made here: https://github.com/Tribler/tribler/pull/7944
2. Using the "trick" for hiding a menu arrow: https://github.com/Tribler/tribler/blob/03adf6a49744bad2a5e914324e713038d66bf10d/src/tribler/gui/qt_resources/mainwindow.ui#L340

The solution is to change QPushButton to QToolButton as it seems to work a bit more correctly in our specific case with hiding the menu indicator:

QToolButton#add_torrent_button {
    border-style: outset;
    border-width: 1px;
    border-radius: 15px;
    border-color: grey;
    margin-left: 15px;
    padding-left: 10px;
    margin-right: 10px;
}
QToolButton::menu-indicator {
    image: none;
    width: 0px;
}

Please note that the first commit is just a reformatting of the entire mainwindow.ui to maintain strict indentation.

[kozlovsky]

When I run Tribler from the main branch from sources on Windows with Russian localization, this is what I see originally: and this is what I see from the PR branch:

It looks like something should still be done with this arrow... (Note that the button is slightly wider, but that in itself is not a problem)

[drew2a]

@kozlovsky thank you for your feedback. Could you please try the latest version of this PR? It seems that QT behaves differently on different OS.

[kozlovsky]

Now, the menu arrow is not visible. But the button's text looks a bit too large as if it were the most important UI element on the page. It looks like the font size is not fixed, but somehow, it depends on the text length and size of additional items like the icon.

[kozlovsky]

Now it looks good!

[drew2a]

@kozlovsky thank you for your help.