RFC: Use mapping parser implementers instead of extending interface to support different versions

[erhathaway]

elastic-composer/src/mapping_parser.ts

Line 36 in 31b3db6

public static flattenMappings710(rawMappings: ESMapping710): Record<string, ESMappingType> {

In the above code, a new method was added to the mapping parser to support a specific Elasticsearch version. This pattern presents issues b/c it requires conditional logic to use the method (you have to know which version you want and which methods go with which version...). The usual solution would be to add a new mapping parser implementer (specific to a ES version) that conforms to the mapping parser interface.

@markrsocialnative @dearsaturn