Cannot construct MessageCatalogManager with Windows paths containing backslashes

[frostmar]

For example, code like this:

const messageCatalogManager = new MessageCatalogManager(path.join(__dirname, 'catalog-index.json'))

When run on Windows gives a path such as: C:\myrepos\test\lib\catalog-index.json, from which MessageCatalogManager cannot find and load file:// protocol message catalogs