begin clearing errors and warning

[u-an-i]

80 % type-based:
added,
Qt:: added,
Qyyy::ENUM changed,
QVector overlaods deleted (is alias of QList),
QzzzLiteral are now simply QzzzString,
QFileInfo constructor around paths,
comparison with letters: 'A' (not "A"),
some new methods ("secsSinceEpoch" instead of "time_t", "setEncoding" instead of "setCodec",
...
some explicit casts (5%)
some msvc #pragmas (5%)
logic adjusment File Dialog (3%),
logic correction SQL (7%) (prepared statement placeholders have no API to get them!)

[u-an-i]

For reference:

[albar965]

Not sure if I want to go the Qt 6 path. Looks like a lot of effort and I expect plenty of side effects. I even don't want to know what the dock window management is doing now. 🙁

[u-an-i]

i leave this PR here in draft state not continuing the upgrade for now.

[albar965]

Let's keep this in mind for a future version. Maybe after 2.8.