DataTable: support UE DataTable: `ue-csv` and `ue-json`

[wenchy]

References

• Data Driven Gameplay Elements
• Data Table
• UE4 / Unreal Engine 4 / Data Tables (CSV & JSON)
• Unreal Engine 5 - How to Create and Use Data Tables (BASICS!)
• How to Use Data Tables in Unreal Engine 5
  
• What Are Structures & Data Tables - Beginners Informational Guide To Unreal Engine 5
• xresloader: 导出为UE支持的CSV或JSON数据和代码

Design

Extend Mode in proto/tableau/protobuf/tableau.proto:

// Sheet mode.
enum Mode {
  ...
  // UE DataTable references:
  //  - https://dev.epicgames.com/documentation/en-us/unreal-engine/data-driven-gameplay-elements-in-unreal-engine
  //  - https://dev.epicgames.com/documentation/en-us/unreal-engine/BlueprintAPI/EditorScripting/DataTable
  MODE_UE_CSV = 10;   // TODO: CSV format of UE DataTable.
  MODE_UE_JSON = 11;  // TODO: JSON format of UE DataTable.
}

For example, metasheet @TABLEAU in workbook:

Sheet	Mode
Skill	MODE_UE_CSV
Buff	MODE_UE_JSON