Implement a public collectMetadata function for telemetry

[paulkaplan]

There is a standard set of project metadata that is sent with telemetry events which is currently created manually, we should move it to the VM where it belongs. Currently this is done on the gui/scratch-desktop branch since only the offline editor uses it. Here is that implementation:

https://github.com/LLK/scratch-gui/compare/scratch-desktop#diff-2e0062a7e2f44684af5a0ef1cf858c52R7

/**
 * Report a telemetry event.
 * @param {string} event - one of `projectWasCreated`, `projectDidLoad`, `projectDidSave`, `projectWasUploaded`
 */
//TODO make a telemetry HOC and move this stuff there
const collectMetadata = function (vm, projectName = '', locale = '') {
    //TODO move most or all of this into a collectMetadata() method on the VM/Runtime
    const metadata = {
        projectName: projectName,
        language: locale,
        spriteCount: 0,
        blocksCount: 0,
        costumesCount: 0,
        listsCount: 0,
        scriptCount: 0,
        soundsCount: 0,
        variablesCount: 0
    };

    for (const target of vm.runtime.targets) {
        ++metadata.spriteCount;
        metadata.blocksCount += Object.keys(target.sprite.blocks._blocks).length;
        metadata.costumesCount += target.sprite.costumes_.length;
        metadata.scriptCount += target.sprite.blocks._scripts.length;
        metadata.soundsCount += target.sprite.sounds.length;
        for (const variableName in target.variables) {
            const variable = target.variables[variableName];
            if (variable.type === 'list') {
                ++metadata.listsCount;
            } else {
                ++metadata.variablesCount;
            }
        }
    }

    return metadata;
};

export default collectMetadata;