Add EigenDDim type

[reyoung]

• Make DDim can convert to EigenDDim without template arguments
• Add VisitEigenDDim helper. User can visit EigenDim by template
  visitor.

[QiJune]

Please refer to PadOp. We must implement a PadFunction with template parameter Rank.
In this pr, we have EigenDDim to avoid using rank in EigenDim. Do we also need EigenDTensor to avoid using rank in EigenTensor?

[paddle-bot-old]

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