Parser: recover on unfinished head pat in members

[auduchinok]

Adds parser recovery for unfinished head patterns in members. pathOp rule inside the pattern didn't recover properly and subsequent code couldn't be parsed too.

type T =
    member this.

()

{ new T with
      member this. }

()

It also adds tests for object expressions.

[auduchinok]

This is also ready. 🙂

[psfinaki]

Thank you!