Migrate the MWE2 formatter to the formatter2 API

[miklossy]

The MWE2 Formatter and the corresponding test cases should be migrated to the formatter2 API infrastructure.

[miklossy]

See also eclipse-archived/xtext-core#1489

[ewillink]

Not "should" be changed, "must" be changed. The new infrastructure does not support the old Formatter consequently ALL primary Xtext related tools that use a formatter MUST be migrated well before the old infrastructure can be deleted.

[miklossy]

The new infrastructure does not support the old Formatter

@ewillink It is possible to use the old formatter with the new workflow, currently, the Eclipse GEF project also uses that combination, see the GenerateDot.mwe2 and DotFormatter files.

[cdietrich]

we should use the new java based if any