Partial Application Syntax: Stage 1 (#9343)

* add partial application syntax and some tests

* remove unnecessary error message and hasPartial function from parseNewArguments

* add types for PartialExpression

* Update the tests

* rename PartialExpression to Partial

* move Partial from expressions to types and rename to ArgumentPlaceholder

* add tests for ArgumentPlaceholder in babel-generator

* rename Partial to ArgumentPlaceholder

* update the tests

* remove alias from the type and undo changes in generated folder

* adds a nice error message

* better definition for the type

* auto-generated files

* update the conditional for allowPlaceholder message and tests

* update CallExpression definition to accept ArgumentPlaceholder

* change description

* clean up

* indent ArgumentPlaceholder entry and revert unwanted changes

packages/babel-plugin-syntax-partial-application/.npmignore

@@ -0,0 +1,3 @@
+src
+test
+*.log

packages/babel-plugin-syntax-partial-application/README.md

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+# @babel/plugin-syntax-partial-application
+
+> Allow parsing of optional properties
+
+See our website [@babel/plugin-syntax-partial-application](https://babeljs.io/docs/en/next/babel-plugin-syntax-partial-application.html) for more information.
+
+## Install
+
+Using npm:
+
+```sh
+npm install --save-dev @babel/plugin-syntax-partial-application
+```
+
+or using yarn:
+
+```sh
+yarn add @babel/plugin-syntax-partial-application --dev
+```

packages/babel-plugin-syntax-partial-application/package.json

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+{
+  "name": "@babel/plugin-syntax-partial-application",
+  "version": "7.2.0",
+  "description": "Allow parsing of partial application syntax",
+  "repository": "https://github.com/babel/babel/tree/master/packages/babel-plugin-syntax-partial-application",
+  "license": "MIT",
+  "publishConfig": {
+    "access": "public"
+  },
+  "main": "lib/index.js",
+  "keywords": [
+    "babel-plugin"
+  ],
+  "dependencies": {
+    "@babel/helper-plugin-utils": "^7.0.0"
+  },
+  "peerDependencies": {
+    "@babel/core": "^7.0.0-0"
+  },
+  "devDependencies": {
+    "@babel/core": "^7.2.0"
+  }
+}

packages/babel-plugin-syntax-partial-application/src/index.js

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+import { declare } from "@babel/helper-plugin-utils";
+
+export default declare(api => {
+  api.assertVersion(7);
+
+  return {
+    name: "syntax-partial-application",
+
+    manipulateOptions(opts, parserOpts) {
+      parserOpts.plugins.push("partialApplication");
+    },
+  };
+});