Indented variable names not highlighted

[awr1]

let
  x = 1
  y = 2

Names like x and y should be highlighted for variables underneath let, var, and const.

[yuutayamada]

I'd fix this, but as far as I remember, this was really difficult to fixing by emacs' regex based fontification.

[krux02]

I think it is possible. I think Multiline Font Lock is the way to approach the problem. But I don't know specifically how to do it.