Revive JavaScript Bindings (#1177)

Summary:
Yoga's JavaScript bindings do not work past Node 10, or on recent versions of Ubuntu even using it. This is due to a reliance on `nbind`, a library which is no longer maintained. `nbind` itself abstracts over `embind` running Emscripten to generate an asm.js build, along with building Node native modules. In the meantime, [yoga-layout-prebuilt](https://www.npmjs.com/package/yoga-layout-prebuilt) has been used by the community instead of the official package.

https://github.com/facebook/yoga/pull/1177 was contributed as a conversion of bindings created using `nbind` to instead use `embind` directly.

I continued building on this to add more:
1. WebAssembly support (required to be async in browsers)
2. CMake + Ninja Build for the 4 flavors
3. TypeScript typings (partially generated)
4. yarn scripts to build (working on macOS, Ubuntu, Windows)
5. A README with some usage and contribution instructions
6. Updated tests to work with Jest, and updated general infra
7. ESLint and clang-format scripts
8. More GitHub actions (and now testing Windows)
9. Probably more I kinda got carried away here lol

The plan is to eventually publish this to NPM, but there is a little bit of work after this before that happens.

Pull Request resolved: https://github.com/facebook/yoga/pull/1177

Test Plan: The bindings pass Jest tests (both manual and generated). GitHub actions added for the different yarn scripts. Did some manual checks on using the library as TS.

Reviewed By: christophpurrer

Differential Revision: D42207782

Pulled By: NickGerleman

fbshipit-source-id: 1dc5ce440f1c2b9705a005bbdcc86f952785d94e

enums.py

@@ -222,38 +222,56 @@ for name, values in sorted(ENUMS.items()):
         f.write("}\n")
 
 # write out javascript file
-with open(root + "/javascript/sources/YGEnums.js", "w") as f:
+with open(root + "/javascript/src_js/generated/YGEnums.js", "w") as f:
     f.write(get_license("js"))
-    f.write("// @flow\n")
-    f.write("// @format\n")
-    f.write("const CONSTANTS = {\n")
+    f.write("module.exports = {\n")
     items = sorted(ENUMS.items())
     for name, values in items:
-        f.write("  %s_COUNT: %s,\n" % (to_java_upper(name), len(values)))
         base = 0
         for value in values:
-            if isinstance(value, tuple):
-                f.write(
-                    "  %s_%s: %d,\n"
-                    % (to_java_upper(name), to_java_upper(value[0]), value[1])
-                )
-                base = value[1] + 1
-            else:
-                f.write(
-                    "  %s_%s: %d,\n" % (to_java_upper(name), to_java_upper(value), base)
-                )
-                base += 1
+            value_arg = value[0] if isinstance(value, tuple) else value
+            ordinal_arg = value[1] if isinstance(value, tuple) else base
+
+            f.write(
+                "  %s_%s: %d,\n"
+                % (to_java_upper(name), to_java_upper(value_arg), ordinal_arg)
+            )
+            base = ordinal_arg + 1
 
         if name != items[-1][0]:
             f.write("\n")
     f.write("};\n")
 
+with open(root + "/javascript/src_js/generated/YGEnums.d.ts", "w") as f:
+    f.write(get_license("js"))
+
     for name, values in sorted(ENUMS.items()):
-        f.write("export type Yoga${} =\n".format(name))
+        base = 0
+        for value in values:
+            value_arg = value[0] if isinstance(value, tuple) else value
+            ordinal_arg = value[1] if isinstance(value, tuple) else base
+
+            f.write(
+                (
+                    "type {name}_{value} = {ordinal} & ['{name}']\n"
+                    + "export const {name}_{value}: {name}_{value};\n\n"
+                ).format(
+                    name=to_java_upper(name),
+                    value=to_java_upper(value_arg),
+                    ordinal=ordinal_arg,
+                )
+            )
+
+            base = ordinal_arg + 1
+
+        f.write("\n")
+
+    for name, values in sorted(ENUMS.items()):
+        f.write("export type {} =\n".format(name))
         for value in values:
             unpackedValue = value[0] if isinstance(value, tuple) else value
             f.write(
-                "  | typeof CONSTANTS.{}_{}".format(
+                "  | typeof {}_{}".format(
                     to_java_upper(name), to_java_upper(unpackedValue)
                 )
             )
@@ -263,4 +281,3 @@ with open(root + "/javascript/sources/YGEnums.js", "w") as f:
                 f.write("\n")
 
         f.write("\n")
-    f.write("module.exports = CONSTANTS;\n")