Update code-comments describing babel plugins (#84622) (#84655)

Author: watson

packages/kbn-babel-preset/common_preset.js

@@ -28,18 +28,19 @@ const plugins = [
   // See https://github.com/babel/proposals/issues/12 for progress
   require.resolve('@babel/plugin-proposal-class-properties'),
 
-  // Optional Chaining proposal is stage 3 (https://github.com/tc39/proposal-optional-chaining)
+  // Optional Chaining proposal is stage 4 (https://github.com/tc39/proposal-optional-chaining)
   // Need this since we are using TypeScript 3.7+
   require.resolve('@babel/plugin-proposal-optional-chaining'),
-  // Nullish coalescing proposal is stage 3 (https://github.com/tc39/proposal-nullish-coalescing)
+
+  // Nullish coalescing proposal is stage 4 (https://github.com/tc39/proposal-nullish-coalescing)
   // Need this since we are using TypeScript 3.7+
   require.resolve('@babel/plugin-proposal-nullish-coalescing-operator'),
 
-  // Proposal is on stage 4 (https://github.com/tc39/proposal-export-ns-from)
+  // Proposal is on stage 4, and included in ECMA-262 (https://github.com/tc39/proposal-export-ns-from)
   // Need this since we are using TypeScript 3.8+
   require.resolve('@babel/plugin-proposal-export-namespace-from'),
 
-  // Proposal is on stage 4 (https://github.com/tc39/proposal-export-ns-from)
+  // Proposal is on stage 4, and included in ECMA-262 (https://github.com/tc39/proposal-export-ns-from)
   // Need this since we are using TypeScript 3.9+
   require.resolve('@babel/plugin-proposal-private-methods'),
 ];