Rewrite turtle upgrade registration to be more data driven (#967)

The feature nobody asked for, but we're getting anyway.

Old way to register a turtle/pocket computer upgrade:

    ComputerCraftAPI.registerTurtleUpgrade(new MyUpgrade(new ResourceLocation("my_mod", "my_upgrade")));

New way to register a turtle/pocket computer upgrade:

First, define a serialiser for your turtle upgrade type:

    static final DeferredRegister<TurtleUpgradeSerialiser<?>> SERIALISERS = DeferredRegister.create( TurtleUpgradeSerialiser.TYPE, "my_mod" );
    public static final RegistryObject<TurtleUpgradeSerialiser<MyUpgrade>> MY_UPGRADE =
        SERIALISERS.register( "my_upgrade", () -> TurtleUpgradeSerialiser.simple( MyUpgrade::new ) );
    SERIALISERS.register(bus); // Call in your mod constructor.

Now either create a JSON string or use a data generator to register your upgrades:

    class TurtleDataGenerator extends TurtleUpgradeDataProvider {
        @Override
        protected void addUpgrades( @Nonnull Consumer<Upgrade<TurtleUpgradeSerialiser<?>>> addUpgrade )
            simple(new ResourceLocation("my_mod", my_upgrade"), MY_UPGRADE.get()).add(addUpgrade);
        }
    }

See much better! In all seriousness, this does offer some benefits,
namely that it's now possible to overwrite or create upgrades via
datapacks.

Actual changes:
 - Remove ComputerCraftAPI.register{Turtle,Pocket}Upgrade functions.

 - Instead add {Turtle,Pocket}UpgradeSerialiser classes, which are used
   to load upgrades from JSON files in datapacks, and then read/write
   them to network packets (much like recipe serialisers).

 - The upgrade registries now subscribe to datapack reload events. They
   find all JSON files in the
   data/$mod_id/computercraft/{turtle,pocket}_upgrades directories,
   parse them, and then register them as upgrades.

   Once datapacks have fully reloaded, these upgrades are then sent over
   the network to the client.

 - Add data generators for turtle and pocket computer upgrades, to make
   the creation of JSON files a bit easier.

 - Port all of CC:T's upgrades over to use the new system.

src/generated/resources/data/computercraft/computercraft/pocket_upgrades/speaker.json

@@ -0,0 +1,4 @@
+{
+  "type": "computercraft:speaker",
+  "item": "computercraft:speaker"
+}

src/generated/resources/data/computercraft/computercraft/pocket_upgrades/wireless_modem_advanced.json

@@ -0,0 +1,4 @@
+{
+  "type": "computercraft:wireless_modem_advanced",
+  "item": "computercraft:wireless_modem_advanced"
+}

src/generated/resources/data/computercraft/computercraft/pocket_upgrades/wireless_modem_normal.json

@@ -0,0 +1,4 @@
+{
+  "type": "computercraft:wireless_modem_normal",
+  "item": "computercraft:wireless_modem_normal"
+}

src/generated/resources/data/computercraft/computercraft/turtle_upgrades/speaker.json

@@ -0,0 +1,4 @@
+{
+  "type": "computercraft:speaker",
+  "item": "computercraft:speaker"
+}

src/generated/resources/data/computercraft/computercraft/turtle_upgrades/wireless_modem_advanced.json

@@ -0,0 +1,4 @@
+{
+  "type": "computercraft:wireless_modem_advanced",
+  "item": "computercraft:wireless_modem_advanced"
+}

src/generated/resources/data/computercraft/computercraft/turtle_upgrades/wireless_modem_normal.json

@@ -0,0 +1,4 @@
+{
+  "type": "computercraft:wireless_modem_normal",
+  "item": "computercraft:wireless_modem_normal"
+}

src/generated/resources/data/minecraft/computercraft/turtle_upgrades/crafting_table.json

@@ -0,0 +1,4 @@
+{
+  "type": "computercraft:workbench",
+  "item": "minecraft:crafting_table"
+}

src/generated/resources/data/minecraft/computercraft/turtle_upgrades/diamond_axe.json

@@ -0,0 +1,5 @@
+{
+  "type": "computercraft:tool",
+  "item": "minecraft:diamond_axe",
+  "damageMultiplier": 6.0
+}

src/generated/resources/data/minecraft/computercraft/turtle_upgrades/diamond_hoe.json

@@ -0,0 +1,5 @@
+{
+  "type": "computercraft:tool",
+  "item": "minecraft:diamond_hoe",
+  "breakable": "computercraft:turtle_hoe_harvestable"
+}

src/generated/resources/data/minecraft/computercraft/turtle_upgrades/diamond_pickaxe.json

@@ -0,0 +1,4 @@
+{
+  "type": "computercraft:tool",
+  "item": "minecraft:diamond_pickaxe"
+}

src/generated/resources/data/minecraft/computercraft/turtle_upgrades/diamond_shovel.json

@@ -0,0 +1,5 @@
+{
+  "type": "computercraft:tool",
+  "item": "minecraft:diamond_shovel",
+  "breakable": "computercraft:turtle_shovel_harvestable"
+}

src/generated/resources/data/minecraft/computercraft/turtle_upgrades/diamond_sword.json

@@ -0,0 +1,6 @@
+{
+  "type": "computercraft:tool",
+  "item": "minecraft:diamond_sword",
+  "damageMultiplier": 9.0,
+  "breakable": "computercraft:turtle_sword_harvestable"
+}