FML: Use FMLParser in StructureMapUtilities and support for identity transform

[oliveregger]

There are currently mutliple parsers for FML, FmlParser which is used by the FHIR Validator and IG Publisher and one in StructureMapUtilities for each FHIR version.

They have slight different behaviour

• FmlParser creates a DefaultAnonymousGroup while the one in StructureMapUtilities did not
• FmlParser has different comment handling

Will provide a PR which uses FmlParser also in StructureMapUtilities for R5 and that the identity transform is running through: https://github.com/FHIR/fhir-test-cases/pull/195

In addition FmlParser will be extended with:

• multiline support for description as described in the spec https://hl7.org/fhir/mapping-language.html#metadata
• support for backtick, quote in source, target rules for the element
• log expression