Allows type checking of unfinished object expressions, like these:

{ new T() }

{ new T(arg1, arg2) }

Before with is typed, this is parsed as a computation expression and these errors are reported:

Expression/Object - Class 16.fs (7,1)-(7,12) typecheck error
  Invalid object expression.
  Objects without overrides or interfaces should use the expression form 'new Type(args)' without braces.

Expression/Object - Class 16.fs (7,1)-(7,12) typecheck error
  Invalid record, sequence or computation expression.
  Sequence expressions should be of the form 'seq { ... }'

The problematic part is neither the type usage, nor the arguments are checked. This PR adds checking of such expressions.

I'm going to look into adding tests later, for now I'd like to see what does CI say about the change.