[fine] Error checking for some cases

fine/tests/expression/errors/class_errors.fine

@@ -0,0 +1,24 @@
+class Point {
+  x: f64;
+  y: f64;
+}
+
+fun test() {
+  let one = new Point { x: 23 };
+  let two = new Point { y: 23 };
+  let three = new Point { y: 23, x: 123, z: "hello" };
+  let four = new Point { y: 23, x: "what" };
+
+  let five = new Point { y: 23, x };
+
+  let x = "now";
+  let six = new Point { y: 23, x };
+}
+
+// @expect-errors:
+// | 7:12: missing an initializer for field y
+// | 8:12: missing an initializer for field x
+// | 9:41: class Point does not have a field named z
+// | 10:32: field x is of type f64, but this expression generates a string
+// | 12:32: cannot find value x here
+// | 15:31: field x is of type f64, but this expression generates a string