Indexes and IDs

[Argmaster]

Currently there is a bit of a mess with indexes (numeric IDs internal to the game and specific to a world) and IDs (universal string identifiers of assets). Tasks are as follows:

• [ ] add dedicated types for representing indexes (eg. see ModelIndex)
• [ ] unify naming of the variables, as currently names like paletteId, stringId, numericId appear all over the place
• [x] incorporate indexes into BaseItem handling #1445
• [ ] incorporate indexes into ToolType handling #1478
• [ ] rename reverseIndices to blocksById, itemsById etc.
• [ ] rename blocks.zig getTypeById to just getById
• [ ] use either getByID or getById consistently

Related to: #1285 Related to: #897