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-parser/src/plugins/estree.js

@@ -43,6 +43,17 @@ export default (superClass: Class<Parser>): Class<Parser> =>
       return node;
     }
 
+    estreeParseDecimalLiteral(value: any): N.Node {
+      // https://github.com/estree/estree/blob/master/experimental/decimal.md
+      // $FlowIgnore
+      // todo: use BigDecimal when node supports it.
+      const decimal = null;
+      const node = this.estreeParseLiteral(decimal);
+      node.decimal = String(node.value || value);
+
+      return node;
+    }
+
     estreeParseLiteral(value: any): N.Node {
       return this.parseLiteral(value, "Literal");
     }
@@ -229,6 +240,9 @@ export default (superClass: Class<Parser>): Class<Parser> =>
         case tt.bigint:
           return this.estreeParseBigIntLiteral(this.state.value);
 
+        case tt.decimal:
+          return this.estreeParseDecimalLiteral(this.state.value);
+
         case tt._null:
           return this.estreeParseLiteral(null);