Fix destruction of Intl Collator and DateTimeFormat

Summary:
Like `NumberFormat`, `Collator` and `DateTimeFormat` also contain JNI
references. So we need to destroy them in a context that is
registered with the JVM.

Reviewed By: Huxpro

Differential Revision: D29005275

fbshipit-source-id: 38c53fad9c20a5146eedd1bd9c403b2bd6d0d46e

lib/Platform/Intl/PlatformIntlAndroid.cpp

@@ -315,7 +315,9 @@ struct Collator::Impl {
 
 Collator::Collator() : impl_(std::make_unique<Impl>()) {}
 
-Collator::~Collator() {}
+Collator::~Collator() {
+  jni::ThreadScope::WithClassLoader([&] { impl_.reset(); });
+}
 
 vm::CallResult<std::vector<std::u16string>> Collator::supportedLocalesOf(
     vm::Runtime *runtime,
@@ -408,7 +410,9 @@ struct DateTimeFormat::Impl {
 
 DateTimeFormat::DateTimeFormat() : impl_(std::make_unique<Impl>()) {}
 
-DateTimeFormat::~DateTimeFormat() {}
+DateTimeFormat::~DateTimeFormat() {
+  jni::ThreadScope::WithClassLoader([&] { impl_.reset(); });
+}
 
 vm::CallResult<std::vector<std::u16string>> DateTimeFormat::supportedLocalesOf(
     vm::Runtime *runtime,