Remove the Base() *BaseExecutor function from Executor interface

[YangKeao]

Enhancement

To eliminate the usage of Ctx from the executors, as the first step, we can remove the abuse of Base() *BaseExecutor from the Executor interface. It can be replaced with

type Executor interface {
	NewChunk() *chunk.Chunk
	NewChunkWithCapacity(fields []*types.FieldType, capacity int, maxCachesize int) *chunk.Chunk

	RuntimeStats() *execdetails.BasicRuntimeStats

	HandleSQLKillerSignal() error
	RegisterSQLAndPlanInExecForTopSQL()

	AllChildren() []Executor

        // ...
}

Actually, some helper functions can be removed, like TryNewCacheChunk, RetTypes... They are just calling the methods of executors after this refractor.

The executors can still use the Ctx inside, by calling .BaseExecutor.Ctx() internally, as it can access the BaseExecutor field and the type of the specific executor is clear.