sql: "internal error: interface conversion: *sql.optView is not cat.Table: missing method Check" when decoding gist

@glennfawcett found this nice one:

```
demo@127.0.0.1:26257/demoapp/defaultdb> select crdb_internal.decode_plan_gist('AgHk/v//nxkAAOAXAAAAAwcKBQobBQQMMAHK////nxkEAJDBAQIAADEFAjEFAjEFAjEFAgcCBgI=');
ERROR: internal error: interface conversion: *sql.optView is not cat.Table: missing method Check
SQLSTATE: XX000
DETAIL: stack trace:
github.com/cockroachdb/cockroach/pkg/util/errorutil/catch.go:29: ShouldCatch()
github.com/cockroachdb/cockroach/pkg/sql/opt/exec/explain/plan_gist_factory.go:172: func1()
GOROOT/src/runtime/panic.go:914: gopanic()
GOROOT/src/runtime/iface.go:92: getitab()
GOROOT/src/runtime/iface.go:430: assertI2I()
github.com/cockroachdb/cockroach/pkg/sql/opt/exec/explain/plan_gist_factory.go:309: decodeTable()
github.com/cockroachdb/cockroach/bazel-out/darwin-fastbuild/bin/pkg/sql/opt/exec/explain/plan_gist_factory.og.go:1145: decodeOperatorBody()
github.com/cockroachdb/cockroach/pkg/sql/opt/exec/explain/plan_gist_factory.go:243: decodeOp()
github.com/cockroachdb/cockroach/pkg/sql/opt/exec/explain/plan_gist_factory.go:216: DecodePlanGistToPlan()
github.com/cockroachdb/cockroach/pkg/sql/opt/exec/explain/plan_gist_factory.go:184: DecodePlanGistToRows()
github.com/cockroachdb/cockroach/pkg/sql/plan_opt.go:735: DecodeGist()
github.com/cockroachdb/cockroach/pkg/sql/sem/builtins/generator_builtins.go:739: Start()
github.com/cockroachdb/cockroach/pkg/sql/rowexec/project_set.go:208: nextInputRow()
github.com/cockroachdb/cockroach/pkg/sql/rowexec/project_set.go:290: Next()
github.com/cockroachdb/cockroach/pkg/sql/colexec/columnarizer.go:239: Next()
github.com/cockroachdb/cockroach/pkg/sql/colflow/stats.go:118: next()
github.com/cockroachdb/cockroach/pkg/sql/colexecerror/error.go:92: CatchVectorizedRuntimeError()
github.com/cockroachdb/cockroach/pkg/sql/colflow/stats.go:126: Next()
github.com/cockroachdb/cockroach/pkg/sql/colflow/flow_coordinator.go:250: nextAdapter()
github.com/cockroachdb/cockroach/pkg/sql/colexecerror/error.go:92: CatchVectorizedRuntimeError()
github.com/cockroachdb/cockroach/pkg/sql/colflow/flow_coordinator.go:254: next()
github.com/cockroachdb/cockroach/pkg/sql/colflow/flow_coordinator.go:286: Run()
github.com/cockroachdb/cockroach/pkg/sql/colflow/vectorized_flow.go:320: Run()
github.com/cockroachdb/cockroach/pkg/sql/distsql_running.go:909: Run()
github.com/cockroachdb/cockroach/pkg/sql/distsql_running.go:1970: PlanAndRun()
github.com/cockroachdb/cockroach/pkg/sql/distsql_running.go:1685: func3()
github.com/cockroachdb/cockroach/pkg/sql/distsql_running.go:1688: PlanAndRunAll()
github.com/cockroachdb/cockroach/pkg/sql/conn_executor_exec.go:2420: execWithDistSQLEngine()
github.com/cockroachdb/cockroach/pkg/sql/conn_executor_exec.go:1949: dispatchToExecutionEngine()
github.com/cockroachdb/cockroach/pkg/sql/conn_executor_exec.go:1125: execStmtInOpenState()
github.com/cockroachdb/cockroach/pkg/sql/conn_executor_exec.go:146: func1()
github.com/cockroachdb/cockroach/pkg/sql/conn_executor_exec.go:3427: execWithProfiling()
```

The statement is:

```
root@localhost:26257/defaultdb> select query from stmt_stats_copy where gist =
-> 'AgHk/v//nxkAAOAXAAAAAwcKBQobBQQMMAHK////nxkEAJDBAQIAADEFAjEFAjEFAjEFAgcCBgI=';
query
-----------------------------------------------------------------------
SELECT create_statement FROM [SHOW CREATE defaultdb.public.measure]
```

Jira issue: CRDB-35938