Add features for the Arithmetic example

[pluralia]

• validation

  • Recursion should not be allowed in arithmetics #1019
  • Improve the "check devided by zero" validator in arithmetics #1025

• code actions

  • Replace expressions that can be folded into a constant with a constant (look at the corresponding validation here)

• LSP

  • Formatter
  • FoldingRangeProvider
  • RenameProvider