Provide utility methods to provide the canonical form of string module identifiers to replace what we get from the deprecated ModuleIdentifier class.

The canonical string representation of a JBoss Modules module identifier is of the form <name>:<slot> unless the slot is "main" in which the form is just <name>.

The deprecated org.jboss.modules.ModuleIdentifier handles that canonical representation internally. For example, ModuleIdentifier.toString() will never output a string ending in ":main". As we remove use of ModuleIdentifier we need our own logic to ensure we use the correct string form of module identifiers. Simply accepting raw string input from external sources is not adequate.