Adding {read,write}Embedded{From,To} methods for hidl_handle

This change implements helper functions for serializing/deserializing
hidl_handle types to/from parcels, similar to the other HIDL types
(hidl_string, hild_string).

Bug: 35098567
Test: Ran the hidl_test suite
Change-Id: I5f6720c42d69a7f760a91442fbdeec202cb2ffcd
diff --git a/base/include/hidl/HidlSupport.h b/base/include/hidl/HidlSupport.h
index 7a5183b..2d0dc25 100644
--- a/base/include/hidl/HidlSupport.h
+++ b/base/include/hidl/HidlSupport.h
@@ -116,6 +116,10 @@
 
     // explicit conversion
     const native_handle_t *getNativeHandle() const;
+
+    // offsetof(hidl_handle, mHandle) exposed since mHandle is private.
+    static const size_t kOffsetOfNativeHandle;
+
 private:
     void freeHandle();