Implement U013: Unnecessary TypedDict syntactic form (#716)

src/python/identifiers.rs

@@ -0,0 +1,5 @@
+use once_cell::sync::Lazy;
+use regex::Regex;
+
+pub static IDENTIFIER_REGEX: Lazy<Regex> =
+    Lazy::new(|| Regex::new(r"^[A-Za-z_][A-Za-z0-9_]*$").unwrap());

src/python/mod.rs

@@ -1,5 +1,6 @@
 pub mod builtins;
 pub mod future;
+pub mod identifiers;
 pub mod keyword;
 pub mod string;
 pub mod sys;