Simplify token context (#13450)

* refactor: unify tc.brace and tc.templateQuasi

* refactor: remove unused context check

* perf: reduce arrayPrototype call and hoist variables

packages/babel-parser/src/tokenizer/state.js

@@ -127,10 +127,10 @@ export default class State {
   lastTokStart: number = 0;
   lastTokEnd: number = 0;
 
-  // The context stack is used to superficially track syntactic
-  // context to predict whether a regular expression is allowed in a
-  // given position.
+  // The context stack is used to track whether the apostrophe "`" starts
+  // or ends a string template
   context: Array<TokContext> = [ct.brace];
+  // Used to track whether a JSX element is allowed to form
   exprAllowed: boolean = true;
 
   // Used to signal to callers of `readWord1` whether the word