[android] - replace platform default implementation using nunicode for uppercasing an lowercasing with an Android specific String.java equivalent

platform/android/src/unaccent.cpp

@@ -0,0 +1,18 @@
+#include <unaccent.hpp>
+#include <string>
+#include "attach_env.hpp"
+#include "text/collator_jni.hpp"
+#include <jni/jni.hpp>
+
+namespace mbgl {
+namespace platform {
+
+std::string unaccent(const std::string& str) {
+    android::UniqueEnv env = android::AttachEnv();
+    jni::Local<jni::String> input = jni::Make<jni::String>(*env, str);
+    jni::Local<jni::String> unaccented = android::StringUtils::unaccent(*env, input);
+    return jni::Make<std::string>(*env, unaccented);
+}
+
+} // namespace platform
+} // namespace mbgl