Remove RecordPattern from the IR

[AttilaMihaly]

Record patterns provide very limited value since you cannot use them to branch out. You can only use them to make the syntax slightly more concise in certain cases. At the same time very few backends will support this and mapping it to existing features will add significant complexity.

If the lack of support ever becomes a limitation for modelers we can easily change the frontend to transparently rewrite usages to the dot notation.

[AttilaMihaly]

For example this snippet:

distance { x, y } =
  sqrt (x^2 + y^2)

Can be rewritten to the following to remove the RecordPattern:

distance p =
  sqrt (p.x^2 + p.y^2)