Leak the global static mutex in CKTextKitContext to avoid static destructor fiasco

Summary:
OSS CK is crashing on the exit. The probable cause is that it is static mutex is destroyed at the same time when another thread tries to lock it.
This diff leaks the mutex in order to avoid that crash

I haven't tested this code, but this is what I would try to resolve #892. Someone should run some smoke tests with something like the above
Closes #906

Reviewed By: kfirapps

Differential Revision: D7616427

Pulled By: gkassabli

fbshipit-source-id: fe4d9fc1add8228d3bd672f853cca8d54a02bc58

Author: ocrickard

ComponentTextKit/TextKit/CKTextKitContext.mm

@@ -30,8 +30,8 @@ - (instancetype)initWithAttributedString:(NSAttributedString *)attributedString
 {
   if (self = [super init]) {
     // Concurrently initialising TextKit components crashes (rdar://18448377) so we use a global lock.
-    static std::mutex __static_mutex;
-    std::lock_guard<std::mutex> l(__static_mutex);
+    static std::mutex *__static_mutex = new std::mutex;
+    std::lock_guard<std::mutex> l(*__static_mutex);
     // Create the TextKit component stack with our default configuration.
     _textStorage = (attributedString ? [[NSTextStorage alloc] initWithAttributedString:attributedString] : [[NSTextStorage alloc] init]);
     _layoutManager = layoutManagerFactory ? layoutManagerFactory() : [[NSLayoutManager alloc] init];