Refactor singe matadata.

[andy840119]

Wnat's should be done in this issue:

• [x] Implement the singer info class. -> Implemented in the #1774
  • [x] should be able to get list of main singer
  • [x] [Optional] should be able to get list of sub-singer by main singer.
  • [x] [Optional] should be able to get IDictionary<Singer, SubSinger[]> by (maybe lyric or singer ids, not really sure)
  • [x] class should have IList<ISinger>? Not really sure should save by sorting or not?
• [x] Apply singer info into the karaoke beatmap. -> Implemented in the #1775
• [x] Guess should write the json convertor for the generic type. -> Implemented in the #1771
• [ ] Not really sure should implement the ICompare<T> to those singer classes?
• [x] Guess should add support-sub-singer flag and should be default as false. -> Added in the #1776.
• [ ] Should be able to get the singer instance directly in the singer class.
• [ ] IList<int> SingersIds should not have the bindable and should be marked as json ignore.

And notice that did not make unnecessary things for sub-singer because not really sure will implement this or not. Might not be that useful i guess.

[andy840119]

Damn, will have those issues:

• We have utils to check if singer instance is in the singer, not really sure should check by singer index or singer instance in the lyric.
• Should separate or combine the lyric should copy the singer instance also?

[andy840119]

Not very sure about last part because it should be possible to get the singer instance by working beatmap 🤔

[andy840119]

Maybe change to the array and use the validator to check if singer instance is being synced or not

[andy840119]

Maybe should make the validator more global? Reference lyric and singer listance will check by the flag