Add more debug output to QEglContext::chooseConfig()

If QEglContext::chooseConfig() fails to find a valid configuration, it prints out the (last) requested configuration and the available configurations.

However, it does not take into account that the original configuration may have been reduced several times (by QEglProperties::reduceConfiguration()), or that the failure of eglChooseConfig() (or other EGL calls) may be associated with helpful error information from eglGetError().

It would therefore be nice if QEglContext::chooseConfig() printed out more debug output while trying different configurations and printed out information about any errors occurring while doing this.