qmlls options incompatibility from 6.8 to 6.9

The p (documents path) parameter of qmlls does not take a value on 6.8. It's being treated as a flag when QCommandLineOption ctor has an empty default value.

From the other hand, this issue has been fixed on 6.9 with:

https://codereview.qt-project.org/c/qt/qtdeclarative/+/603035

by adding a valueName and also changing p to d as a more meaningful letter.

To keep 6.9 version compatible with 6.8 and also keep them source compatible we can:

1. Fix the problem on 6.8 as it's an LTS ( by adding a valueName to QCLO but keeping the option as p)
2. Add "p" to the same QCLO as "d" on 6.9, making it backward compatible with 6.8. (https://doc.qt.io/qt-6/qcommandlineoption.html#QCommandLineOption-4)