Add dedicated items for equipment upgrades

[Dinopony]

Add dedicated items for equipment upgrades:

• "Sword upgrade" (uses Sword sprite)
• "Armor upgrade" (uses Ancient Armor sprite)
• "Flail upgrade" (uses Iron Flail sprite)
• "Bow upgrade" (uses Bow sprite)
• "Boots upgrade" (uses Long Boots sprite)
• "X Magic upgrade" (uses X Scroll sprite)

These items will have the same slot ID as items from the matching category, and will have a very high tier (10+) to be unreachable. They will fill unused item IDs, and packing them could help in the progressive items function to filter item IDs to process.

[Dinopony]

Pre-work done in 6ab593c to facilitate further work

[Dinopony]

Added in 2f933f3