support multi-valued index

[xiongjiwei]

The multi-valued index is introduced by mysql8.0, and there are users who want to use this feature in tidb #7968 (comment)

Task

• Expression M
  • Parser: new cast as array syntax #39821
  • Type: introduce new typed_array type #40045
  • Expression: new function to cast json to typed_array #40128
  • Expression: new json function member of json_overlaps #39866
• DML/DDL 1.5M
  • Insert/delete/update handle the mv index, including DDL #40207
  • Create/alter mv index, check the restriction #40086
  • Online create multi-valued index #40337
• Optimizer M
  • planner: support converting json_memberof/overlaps/contains to IndexMerge to access MVIndex #40191
  • Explain the plan
• Misc S
  • support admin check table on multi-valued index #40272
  • support cleanup mv-index #40427
  • support recover multi-valued index #41180
• Known bugs
  • read multi-valued index get wrong result if using char(N) #40558
  • Get different result from MySQL when using multi-valued index #40529

Phase 2 (GA)

• tools test about multi-valued index #42037
• support double-array type index #42142
• optimize update array performance #41619
• enhance optimizer to support more complex condition
• add design doc on GitHub about multi-valued index #42208
• enhance random tests