Death messages aren't saved to NBT

The Bug:

Death messages aren't saved to NBT.

As a result of this issue, death messages aren't displayed on the death screen when the player's NBT data is reloaded. For example, if a player dies, exits to the title screen, and rejoins the world, no death message (cause of death) would be presented to them on the death screen. This can also be seen if a dead player were to change dimensions.

Steps to Reproduce:

1. Die through any method.

2. While on the death screen, click on the "Title Screen" button and return to the title screen.

3. Load into the world again and look at the death screen.

4. Take note as to whether or not death messages are saved to NBT.

Observed Behavior:

Death messages aren't saved to NBT.

Expected Behavior:

Death messages would be saved to NBT.