[monodroid] Glue and utilities code changes for C++-ification (#2611)

As part of our continued "C++ification" effort (434d2d8, etc.),
additional cleanups for `src/monodroid`:

  * Use `new/new[]/delete/delete[]` more
  * Avoid calling the `printf()` family of functions in favor of new,
    template `Utils.string_concat()` member function.
    When `sprintf()` is used to concatenate just strings we can do
    better by not calling the C varargs functions and generate very
    efficient code.
  * Replace C `strdup()` calls with `Utils.strdup_new()`, which uses
    `new char[]` to allocate memory.

Author: grendello

src/monodroid/jni/embedded-assemblies.cc

@@ -53,7 +53,7 @@ void EmbeddedAssemblies::set_assemblies_prefix (const char *prefix)
 {
 	if (assemblies_prefix_override != nullptr)
 		delete[] assemblies_prefix_override;
-	assemblies_prefix_override = prefix != nullptr ? strdup (prefix) : nullptr;
+	assemblies_prefix_override = prefix != nullptr ? utils.strdup_new (prefix) : nullptr;
 }
 
 MonoAssembly*

src/monodroid/jni/embedded-assemblies.h

@@ -83,5 +83,4 @@ namespace xamarin { namespace android { namespace internal {
 }}}
 
 MONO_API int monodroid_embedded_assemblies_set_assemblies_prefix (const char *prefix);
-
 #endif /* INC_MONODROID_EMBEDDED_ASSEMBLIES_H */