Update upstream B/CB/S

--- work/Bukkit
Submodule work/Bukkit 6eac6d70..1ef8b9d9:
  > Add Player#openBook(ItemStack) method

--- work/CraftBukkit
Submodule work/CraftBukkit 17543ecf..649921e5:
  > Add Player#openBook(ItemStack) method
  > SPIGOT-2000: Picking up items to shield slot working inconsistently when inventory is full
  > SPIGOT-5037: Player.openMerchant does not show merchant level
  > SPIGOT-5038: Inventory.getHolder returns null for wandering traders

--- work/Spigot
Submodule work/Spigot baafee91..df0eb250:
  > SPIGOT-5043: Desync if world is changed in PlayerSpawnLocationEvent
  > Rebuild patches

Implementation developer note:
This patch adds a "pre-source" patch system for fixing malformed patches
from upstream directly. This seems to keep happening so it's best we
have some way to deal with them. This system brings those issues into
our domain rather than needing to wait for upstream to fix their
malformed files.

work/pre-source-patches/Fix-PlayerInventory-file.patch

@@ -0,0 +1,29 @@
+--- work/CraftBukkit/nms-patches/PlayerInventory.patch	2019-06-08 15:17:36.377383665 -0500
++++ work/CraftBukkit/nms-patches/PlayerInventory.patch	2019-06-08 15:17:36.377383665 -0500
+@@ -0,0 +0,0 @@
+      public PlayerInventory(EntityHuman entityhuman) {
+          this.items = NonNullList.a(36, ItemStack.a);
+          this.armor = NonNullList.a(4, ItemStack.a);
+-@@ -0,0 +0,0 @@
++@@ -0,0 +0,0 @@
+          return itemstack.getItem() == itemstack1.getItem() && ItemStack.equals(itemstack, itemstack1);
+      }
+  
+@@ -0,0 +0,0 @@
+      public int getFirstEmptySlotIndex() {
+          for (int i = 0; i < this.items.size(); ++i) {
+              if (((ItemStack) this.items.get(i)).isEmpty()) {
+-@@ -0,0 +0,0 @@
++@@ -0,0 +0,0 @@
+                  ItemStack itemstack = (ItemStack) this.armor.get(i);
+  
+                  if (itemstack.getItem() instanceof ItemArmor) {
+@@ -0,0 +0,0 @@
+                      });
+                  }
+              }
+-@@ -0,0 +0,0 @@
++@@ -0,0 +0,0 @@
+      }
+  
+      public ItemStack getCarried() {