Merging 2 Modelica files

[sjoelund]

OpenModelica has:

Interface
function diffModelicaFileListings
  input String before;
  input String after;
  input DiffFormat diffFormat = DiffFormat.color;
  input Boolean failOnSemanticsChange = false "Defaults to returning after instead of hard fail";
  output String result;
end diffModelicaFileListings;

Creates diffs of two strings (before and after) corresponding to Modelica files. The diff is specialized to handle the [list](https://build.openmodelica.org/Documentation/OpenModelica.Scripting.list.html) API moving comments around in the file and introducing or deleting whitespace.

The output can be chosen to be a colored diff (for terminals), XML, or the final text (deletions removed).

The same functionality would be good to have in the language server. We have testcases in https://github.com/OpenModelica/OpenModelica/tree/master/testsuite/openmodelica/diff

And the implementation is in:
https://github.com/OpenModelica/OpenModelica/blob/master/OMCompiler/Compiler/Parsers/SimpleModelicaParser.mo
https://github.com/OpenModelica/OpenModelica/blob/master/OMCompiler/Compiler/Util/DiffAlgorithm.mo

The grammar itself should not be all too dissimilar to the tree sitter grammar