hidden column don't have to own its virtual expression when its a stored type

[AilinKid]

Enhancement

here give a strong assertion that hidden column must have a virtual expression

while only the non-stored 的 column can have its own virtual expression

Reproduce Steps

change one line of the hiddenColumnTests as below

and you got:

Received unexpected error:
        	            	runtime error: invalid memory address or nil pointer dereference
        	            	github.com/pingcap/errors.AddStack
        	            		/Users/arenatlx/go/pkg/mod/github.com/pingcap/[email protected]/errors.go:178
        	            	github.com/pingcap/errors.Trace
        	            		/Users/arenatlx/go/pkg/mod/github.com/pingcap/[email protected]/juju_adaptor.go:15
        	            	github.com/pingcap/tidb/pkg/util.GetRecoverError
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/util/util.go:303
        	            	github.com/pingcap/tidb/pkg/executor/internal/exec.Next.func1
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/executor/internal/exec/executor.go:387
        	            	runtime.gopanic
        	            		/opt/homebrew/opt/go/libexec/src/runtime/panic.go:920
        	            	runtime.panicmem
        	            		/opt/homebrew/opt/go/libexec/src/runtime/panic.go:261
        	            	runtime.sigpanic
        	            		/opt/homebrew/opt/go/libexec/src/runtime/signal_unix.go:861
        	            	github.com/pingcap/tidb/pkg/expression.(*Column).String
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/expression/column.go:395
        	            	github.com/pingcap/tidb/pkg/expression.ExplainExpressionList
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/expression/explain.go:160
        	            	github.com/pingcap/tidb/pkg/planner/core.(*LogicalProjection).ExplainInfo
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/planner/core/explain.go:916
        	            	github.com/pingcap/tidb/pkg/planner/core.(*baseLogicalPlan).BuildPlanTrace
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/planner/core/plan.go:856
        	            	github.com/pingcap/tidb/pkg/planner/core.(*logicalOptimizeOp).appendBeforeRuleOptimize
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/planner/core/optimizer.go:149
        	            	github.com/pingcap/tidb/pkg/planner/core.logicalOptimize
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/planner/core/optimizer.go:1181
        	            	github.com/pingcap/tidb/pkg/planner/core.doOptimize
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/planner/core/optimizer.go:321
        	            	github.com/pingcap/tidb/pkg/planner/core.DoOptimize
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/planner/core/optimizer.go:383
        	            	github.com/pingcap/tidb/pkg/planner/core.(*PlanBuilder).buildDelete
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/planner/core/logical_plan_builder.go:6230
        	            	github.com/pingcap/tidb/pkg/planner/core.(*PlanBuilder).Build
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/planner/core/planbuilder.go:507
        	            	github.com/pingcap/tidb/pkg/planner.buildLogicalPlan
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/planner/optimize.go:548
        	            	github.com/pingcap/tidb/pkg/planner.optimize
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/planner/optimize.go:465
        	            	github.com/pingcap/tidb/pkg/planner.Optimize
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/planner/optimize.go:333
        	            	github.com/pingcap/tidb/pkg/executor.(*TraceExec).nextOptimizerPlanTrace
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/executor/trace.go:186
        	            	github.com/pingcap/tidb/pkg/executor.(*TraceExec).Next
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/executor/trace.go:91
        	            	github.com/pingcap/tidb/pkg/executor/internal/exec.Next
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/executor/internal/exec/executor.go:403
        	            	github.com/pingcap/tidb/pkg/executor.(*ExecStmt).next
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/executor/adapter.go:1206
        	            	github.com/pingcap/tidb/pkg/executor.(*recordSet).Next
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/executor/adapter.go:158
        	            	github.com/pingcap/tidb/pkg/session.GetRows4Test
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/session/tidb.go:346
        	            	github.com/pingcap/tidb/pkg/session.ResultSetToStringSlice
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/session/tidb.go:364
        	            	github.com/pingcap/tidb/pkg/testkit.(*TestKit).ResultSetToResultWithCtx
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/testkit/testkit.go:253
        	            	github.com/pingcap/tidb/pkg/testkit.(*TestKit).MustQueryWithContext
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/testkit/testkit.go:179
        	            	github.com/pingcap/tidb/pkg/testkit.(*TestKit).MustQuery
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/testkit/testkit.go:154
        	            	github.com/pingcap/tidb/pkg/table/tables_test.TestHiddenColumn
        	            		/Users/arenatlx/go/src/github.com/pingcap/tidb/pkg/table/tables/tables_test.go:547
        	            	testing.tRunner
        	            		/opt/homebrew/opt/go/libexec/src/testing/testing.go:1595
        	Test:       	TestHiddenColumn