LibJS: Use copy_data_block_bytes() instead of overwrite() and copy_to()

Replaces usage of ByteBuffer::overwrite() and combinations of
Span::slice() + Span::copy_to() with AO CopyDataBlockBytes.

Userland/Libraries/LibJS/Runtime/ArrayBuffer.cpp

@@ -176,8 +176,7 @@ ThrowCompletionOr<ArrayBuffer*> clone_array_buffer(VM& vm, ArrayBuffer& source_b
     auto& target_block = target_buffer->buffer();
 
     // 5. Perform CopyDataBlockBytes(targetBlock, 0, srcBlock, srcByteOffset, srcLength).
-    // FIXME: This is only correct for ArrayBuffers, once SharedArrayBuffer is implemented, the AO has to be implemented
-    target_block.overwrite(0, source_block.offset_pointer(source_byte_offset), source_length);
+    copy_data_block_bytes(target_block, 0, source_block, source_byte_offset, source_length);
 
     // 6. Return targetBuffer.
     return target_buffer;

Userland/Libraries/LibJS/Runtime/ArrayBufferPrototype.cpp

@@ -115,10 +115,13 @@ JS_DEFINE_NATIVE_FUNCTION(ArrayBufferPrototype::slice)
         return vm.throw_completion<TypeError>(ErrorType::DetachedArrayBuffer);
 
     // 24. Let fromBuf be O.[[ArrayBufferData]].
+    auto& from_buf = array_buffer_object->buffer();
+
     // 25. Let toBuf be new.[[ArrayBufferData]].
+    auto& to_buf = new_array_buffer_object->buffer();
+
     // 26. Perform CopyDataBlockBytes(toBuf, 0, fromBuf, first, newLen).
-    // FIXME: Implement this to specification
-    array_buffer_object->buffer().span().slice(first, new_length).copy_to(new_array_buffer_object->buffer().span());
+    copy_data_block_bytes(to_buf, 0, from_buf, first, new_length);
 
     // 27. Return new.
     return new_array_buffer_object;