Update Custom Crops Tutorial

[QuazChick]

• Custom crops updated to format version 1.21.0.
• Custom seeds and food updated to format version 1.20.80.
• Renamed wiki:growth_stage state to wiki:growth to better match vanilla.
• Growth state range changed from 0-3 to 0-7 to better match vanilla.
  • Selection boxes and growth rate now match vanilla.
• Added wiki:custom_crop_growth custom block component.
• Added dedicated "Issues" section rather than discussing issues throughout the tutorial.
• Split custom dirt blocks off into a new custom-dirt.md page (the custom dirt and farmland blocks still need to be updated).