Add test utilities for C++ and Java

Summary:
@public

Test utility on top of the new event system that maintains a counter of instantiated nodes. Meant to replace the global node counter.

Reviewed By: SidharthGuglani

Differential Revision: D15174855

fbshipit-source-id: 6998472f95a09b8da652257a26596164bdcf43d6

tools/build_defs/oss/yoga_defs.bzl

@@ -148,6 +148,9 @@ def _single_subdir_glob(dirpath, glob_pattern, exclude = None, prefix = None):
 def yoga_dep(dep):
     return "//" + dep
 
+def yoga_cxx_lib(lib):
+    return yoga_dep(lib)
+
 def yoga_android_aar(*args, **kwargs):
     native.android_aar(*args, **kwargs)