checker: check anon struct field valid case (partial fix of #24284) (#24286)

Author: Delta456

vlib/v/checker/checker.v

@@ -602,13 +602,18 @@ fn (mut c Checker) alias_type_decl(mut node ast.AliasTypeDecl) {
 				}
 				if parent_typ_sym.info.is_anon {
 					for field in parent_typ_sym.info.fields {
+						mut is_embed := false
 						field_sym := c.table.sym(field.typ)
 						if field_sym.info is ast.Alias {
 							if c.table.sym(field_sym.info.parent_type).kind != .struct {
 								c.error('cannot embed non-struct `${field_sym.name}`',
 									field.type_pos)
+								is_embed = true
 							}
 						}
+						if !is_embed {
+							c.check_valid_snake_case(field.name, 'field name', field.pos)
+						}
 					}
 				}
 			}

vlib/v/checker/tests/type_alias_struct_invalid_field_naming.out

@@ -0,0 +1,6 @@
+vlib/v/checker/tests/type_alias_struct_invalid_field_naming.vv:2:2: error: field name `field_One` cannot contain uppercase letters, use snake_case instead
+    1 | type Struct = struct {
+    2 |     field_One int
+      |     ~~~~~~~~~~~~~
+    3 |     field_two int
+    4 | }

vlib/v/checker/tests/type_alias_struct_invalid_field_naming.vv

@@ -0,0 +1,4 @@
+type Struct = struct {
+	field_One int
+	field_two int
+}