Improve error message when using keyword as field name

[zth]

Adding a field name that's a keyword like type gives a very cryptic error:

type record ={
  id: string,
  type: int
}

Syntax Errors
The code is not valid ReScript syntax.
[E] Line 2, column 13:
Did you forget a `}` here?
[E] Line 3, column 6:
I'm not sure what to parse here when looking at ":".
[E] Line 4, column 0:
I'm not sure what to parse here when looking at "}".

We should be able to say what the problem is here (keyword as field name)? And suggest a fix (like @as("type") type_).

There are probably more cases like this when keywords are used in places they shouldn't be.