seems `writeBufs.IndexValsBuf` in `TableCommon.addIndices` is not reused.

[lcwangchao]

Enhancement

See:

tidb/pkg/table/tables/tables.go

Line 1109 in a48a4a2

indexVals, err := v.FetchValues(r, indexVals)

The indexVals is assigned using := that makes it a new variable and shadows the outside declaration.

writeBufs.IndexValsBuf is always nil and the []types.Datum will be allocated every time.

[lcwangchao]

It is introduced by #18372 when refactoring code.