[Regression] Several issues in the Symbian FEP integration

Originally taken from QTBUG-12949:

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While testing this I actually found several issues with this test app:

#include <QtGui>

int main(int argc, char **argv)
{
    QApplication app(argc, argv);
    QWidget w;
    QLayout *l = new QVBoxLayout;
    w.setLayout(l);
    QLineEdit *le = new QLineEdit("Test");
    l->addWidget(le);
    le->setEchoMode(QLineEdit::Password);
    le->setMaxLength(8);
    w.show();

    return app.exec();
}

First of all, use N97 for testing.

a)
1. Type a character using the qwerty keyboard.
2. The character replaces the last character.
b)
1. Do a) once more.
2. Then erase everything using backspace.
3. Type a character.
4. Crash!
c)
1. Use qwerty keyboard to type all 8 characters.
2. A ninth character can now be typed for a brief moment, despite 8 being the max length.
3. The type of character is not correct either (try H, for example).
d)
1. Do c) using the virtual keyboard.
2. Again, one more character can be entered, and the display goes out of sync with the actual widget (9 vs 8 characters)