entc/gen: adding tagLookup / strings.Split functions to template engine

Signed-off-by: Alex Snast <alexsn@fb.com>

entc/gen/func.go

@@ -51,6 +51,8 @@ var (
 		"trimPackage": trimPackage,
 		"xtemplate":   xtemplate,
 		"hasTemplate": hasTemplate,
+		"split":       strings.Split,
+		"tagLookup":   tagLookup,
 	}
 	rules   = ruleset()
 	acronym = make(map[string]bool)
@@ -306,3 +308,9 @@ func indirect(v reflect.Value) reflect.Value {
 	}
 	return v
 }
+
+// tagLookup returns the value associated with key in the tag string.
+func tagLookup(tag, key string) string {
+	v, _ := reflect.StructTag(tag).Lookup(key)
+	return v
+}