In-place JS environment

Summary:
This change restructures the package to try to remove the JS build step from the inner loop. Instead, we have a single `src` directory that we babel transform when using, then apply the same transform inline during prepublish.

At the end, we will be publishing a source directory with Babel transformed TS, JS, and TS declarations.

We do a little spring cleaning when doing this. Fixing up some of the folder/file conventions, and removing the non-export-map fallbacks.

We cannot remove the need for a native build.

Reviewed By: yungsters

Differential Revision: D45682153

fbshipit-source-id: ea2dd75c2dd6e3529b1ef6cf6ac6a64a270049a4

javascript/src/Config.h

@@ -0,0 +1,47 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+#include <yoga/Yoga.h>
+
+class Config {
+
+  friend class Node;
+
+public:
+  static Config* create(void);
+
+  static void destroy(Config* config);
+
+private:
+  Config(void);
+
+public:
+  ~Config(void);
+
+public: // Prevent accidental copy
+  Config(Config const&) = delete;
+
+  Config const& operator=(Config const&) = delete;
+
+public: // Setters
+  void setExperimentalFeatureEnabled(int feature, bool enabled);
+  void setPointScaleFactor(float pixelsInPoint);
+  void setUseLegacyStretchBehaviour(bool useLegacyStretchBehaviour);
+  void setErrata(int errata);
+  void setUseWebDefaults(bool useWebDefaults);
+
+public: // Getters
+  bool isExperimentalFeatureEnabled(int feature) const;
+  bool useLegacyStretchBehaviour() const;
+  int getErrata() const;
+  bool useWebDefaults() const;
+
+private:
+  YGConfigRef m_config;
+};