Windeployqt: Add a switch to control timeout for qmlimportscanner

Suggestion:

Add a switch to windeployqt to control qmlimportscanner timeout.

Document the possibility of a timeout and explain workarounds.

Improve logging from windeployqt (=> explain the root cause of the timeout, offer solutions).

A switch to skip scanning certain directories would help too.

Background:

Current implementation of windeployqt can cause qmlimportscanner to timeout.

It looks like the current implementation of windeployqt uses QProcess to run qmlimportscanner like so:

    QProcess process;
    process.setProgram(binary);
    process.setArguments(args);
    process.setWorkingDirectory(workingDirectory);    // Output the command if requested.
    if (optVerboseLevel > 1) {
        QString commandLine;
        appendToCommandLine(binary, &commandLine);
        for (const QString &a : args)
            appendToCommandLine(a, &commandLine);
        std::wcout << "Running: " << commandLine << '\n';
    }    process.start();
    if (!process.waitForStarted() || !process.waitForFinished()) {
        if (errorMessage)
            *errorMessage = process.errorString();
        return false;
    }

and it calls "waitForFinished" for the qmlimportscanner process. QProcess::waitForFinished has a 30 second timeout by default which is probably more than enough for 95% of projects, however, if the project is either huge or the project directory happens to contain e.g. build artifacts, qmlimportscanner may require more than 30 seconds to run in which case a timeout occurs and deployment fails.

It should be noted that Qt Creator creates the build directory within the source directory by default. So, if a user uses Qt Creator with default settings to build and then deploys while passing source root as --qmldir, it is very likely that qmlimportscanner ends up scanning unnecessary stuff and the chances for a timeout occurring significantly increase.