3.0: Multi Language cannot handle file renames

[cdietrich]

having more than one language leads to service registry use the map and not the singleton.
if you rename a file from as dsl file extension to a non dsl file extension (.hello to .hello_bak) this will
lead to the language server crashing cause the update call is called with the new file extension,
which is not in the registry (of course)
cause it is not a dsl extension.

unfortunately the documentupdatehandler is not exported so i cannot do some fuzzing workaround in a subclass

did not test if renaming from one extension of a dsl to another one will leave dead bodies in the index.