Add decimal parsing support (#11640)

* docs: add DecimalLiteral to AST spec

* add decimal support

* fix: throw invalid decimal on start

* add DecimalLiteral type definitions

* update parser typings

* add generator support

* add syntax-decimal plugin

* Add syntax-decimal to babel-standalone

* add syntax-decimal to missing plugin helpers

* fix incorrect test macro

packages/babel-core/src/parser/util/missing-plugin-helper.js

@@ -31,6 +31,12 @@ const pluginNameMap = {
       url: "https://git.io/JvpRG",
     },
   },
+  decimal: {
+    syntax: {
+      name: "@babel/plugin-syntax-decimal",
+      url: "https://git.io/JfKOH",
+    },
+  },
   decorators: {
     syntax: {
       name: "@babel/plugin-syntax-decorators",