gentest for Java and C#

Summary:
- Revise scripts to generate Java and C# unittests using the same HTML fixtures as well as C for code coverage.
- Add wrap_column test workaround in gentest.js.
- Add checkDefaultValues for sanity check of the CSSLayout default values by test-template.html
- Add `align-content: flex-start;` in default div to align with CSSLayout default

    $ cd csharp/gentest
    $ ruby gentest.rb

- macOS example for C#

    $ cd csharp/tests/Facebook.CSSLayout
    $ clang -DCSS_ASSERT_FAIL_ENABLED -Wall -Wextra -dynamiclib -o libCSSLayout.dylib -g -I../../.. ../../../CSSLayout/*.c ../../CSSLayout/CSSInterop.cpp
    $ mcs -debug -t:library -r:nunit.framework.dll -out:CSSLayoutTest.dll *.cs ../../../csharp/Facebook.CSSLayout/*cs
    $ mono64 --debug nunit-console.exe CSSLayoutTest.dll

Reviewed By: emilsjolander

Differential Revision: D4053777

fbshipit-source-id: 84450208015e65baf604987bd56c6a268598b545

tests/CSSLayoutFlexWrapTest.cpp

@@ -40,11 +40,6 @@
  *
  */
 
-// These tests were modified after generation due to both safari and chrome not abiding
-// by the specification. The undefined dimension of a parent should be defined by the total size
-// of their children in that dimension.
-// See diagram under flex-wrap header https://www.w3.org/TR/css-flexbox-1/
-
 #include <CSSLayout/CSSLayout.h>
 #include <gtest/gtest.h>