checker: refactor string to enum error check, handle EnumName(string_variable) too (#20210)

Author: Delta456

vlib/v/checker/checker.v

@@ -3318,8 +3318,8 @@ fn (mut c Checker) cast_expr(mut node ast.CastExpr) ast.Type {
 				}
 			}
 		}
-		if mut node.expr is ast.StringLiteral {
-			c.add_error_detail('use ${c.table.type_to_str(node.typ)}.from_string(\'${node.expr.val}\') instead')
+		if node.expr_type == ast.string_type_idx {
+			c.add_error_detail('use ${c.table.type_to_str(node.typ)}.from_string(${node.expr}) instead')
 			c.error('cannot cast `string` to `enum`', node.pos)
 		}
 	}

vlib/v/checker/tests/string_to_enum_cast_err.out

@@ -3,5 +3,13 @@ vlib/v/checker/tests/string_to_enum_cast_err.vv:8:7: error: cannot cast `string`
     7 | fn main() {
     8 |     _ := Test('one')
       |          ~~~~~~~~~~~
-    9 | }
+    9 |     
+   10 |     my_str := 'one'
 Details: use main.Test.from_string('one') instead
+vlib/v/checker/tests/string_to_enum_cast_err.vv:11:7: error: cannot cast `string` to `enum`
+    9 |     
+   10 |     my_str := 'one'
+   11 |     _ := Test(my_str)
+      |          ~~~~~~~~~~~~
+   12 | }
+Details: use main.Test.from_string(my_str) instead

vlib/v/checker/tests/string_to_enum_cast_err.vv

@@ -6,4 +6,7 @@ enum Test {
 
 fn main() {
 	_ := Test('one')
+	
+	my_str := 'one'
+	_ := Test(my_str)
 }