Convert @babel/traverse to TypeScript (#12488)

Co-authored-by: Nicolò Ribaudo <nicolo.ribaudo@gmail.com>

packages/babel-types/src/traverse/traverse.ts

@@ -40,9 +40,9 @@ export default function traverse<T>(
 
 function traverseSimpleImpl<T>(
   node: any,
-  enter: Function | undefined | null,
-  exit: Function | undefined | null,
-  state: T | undefined | null,
+  enter: Function | undefined,
+  exit: Function | undefined,
+  state: T | undefined,
   ancestors: TraversalAncestors,
 ) {
   const keys = VISITOR_KEYS[node.type];

packages/babel-types/src/validators/isType.ts

@@ -14,10 +14,7 @@ export default function isType(
 /**
  * Test if a `nodeType` is a `targetType` or if `targetType` is an alias of `nodeType`.
  */
-export default function isType(
-  nodeType: string | undefined | null,
-  targetType: string,
-): boolean {
+export default function isType(nodeType: string, targetType: string): boolean {
   if (nodeType === targetType) return true;
 
   // This is a fast-path. If the test above failed, but an alias key is found, then the