PreserveFieldNumbers not works on enum definition or union oneof enum

[wenchy]

Related PR:

• protogen: add option PreserveFieldNumbers to support field's Tag Number compatibility #358

enum RankType {
  option (tableau.etype) = {name:"EnumDefault" note:"榜单类型"};
 
  RANK_TYPE_INVALID = 0;
  RANK_TYPE_PVP = 1 [(tableau.evalue).name = "PVP"];
  RANK_TYPE_PVE = 2 [(tableau.evalue).name = "PVE"];
  RANK_TYPE_ARENA = 3 [(tableau.evalue).name = "ARENA"];
}

If enum value PVE is removed, then ->

enum RankType {
  option (tableau.etype) = {name:"EnumDefault" note:"榜单类型"};
 
  RANK_TYPE_INVALID = 0;
  RANK_TYPE_PVP = 1 [(tableau.evalue).name = "PVP"];
  RANK_TYPE_ARENA = 3 [(tableau.evalue).name = "ARENA"];
}

No reseve tag ids are added.