checker: add a suggestion for misspelled struct field name errors

vlib/v/checker/checker.v

@@ -1673,6 +1673,11 @@ pub fn (mut c Checker) selector_expr(mut selector_expr ast.SelectorExpr) table.T
 			c.error('`$sym.source_name` is not a struct', selector_expr.pos)
 		}
 	} else {
+		if sym.kind == .struct_ {
+			sss := sym.info as table.Struct
+			suggestion := util.new_suggestion(field_name, sss.fields.map(it.name))
+			c.error(suggestion.say(unknown_field_msg), selector_expr.pos)
+		}
 		c.error(unknown_field_msg, selector_expr.pos)
 	}
 	return table.void_type

vlib/v/checker/tests/unknown_struct_field_suggest_name.out

@@ -0,0 +1,8 @@
+vlib/v/checker/tests/unknown_struct_field_suggest_name.vv:11:16: error: type `Points` has no field or method `xxxa`.
+Did you mean `xxxx`?
+    9 |     p := Points{[1], [2], [3]}
+   10 |     println('p: $p')
+   11 |     for x in p.xxxa {
+      |                ~~~~
+   12 |         println('x: $x')
+   13 |     }

vlib/v/checker/tests/unknown_struct_field_suggest_name.vv

@@ -0,0 +1,14 @@
+
+struct Points {
+	xxxx   []int
+	yyyy   []int
+	zzzz   []int
+}
+
+fn main() {
+	p := Points{[1], [2], [3]}
+	println('p: $p')
+    for x in p.xxxa {
+    	println('x: $x')
+    }
+}