sql: PREPARE q AS DROP TYPE typ causes an internal error

[rafiss]

This is affecting master right now, and is causing Random Syntax Tests to fail: https://teamcity.cockroachdb.com/viewLog.html?buildId=2725105&buildTypeId=Cockroach_Nightlies_RandomSyntaxTests

It seems like the issue is that planner.Annotations() is nil when calling connExecutor.addPreparedStmt().

Repro:

root@:26257/defaultdb> create type type_a as enum ('a');
CREATE TYPE

Time: 311ms total (execution 311ms / network 0ms)

root@:26257/defaultdb>
root@:26257/defaultdb> prepare q as drop type type_a;
ERROR: internal error: no Annotations provided
SQLSTATE: XX000
DETAIL: stack trace:
github.com/cockroachdb/cockroach/pkg/sql/sem/tree/format.go:247: NewFmtCtxEx()
github.com/cockroachdb/cockroach/pkg/sql/sem/tree/format.go:412: AsStringWithFQNames()
github.com/cockroachdb/cockroach/pkg/sql/drop_type.go:112: DropType()
github.com/cockroachdb/cockroach/pkg/sql/opaque.go:148: planOpaque()
github.com/cockroachdb/cockroach/pkg/sql/opaque.go:61: buildOpaque()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/opaque.go:69: tryBuildOpaque()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/builder.go:348: buildStmt()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/builder.go:229: buildStmtAtRoot()
github.com/cockroachdb/cockroach/pkg/sql/opt/optbuilder/builder.go:200: Build()
github.com/cockroachdb/cockroach/pkg/sql/plan_opt.go:380: buildReusableMemo()
github.com/cockroachdb/cockroach/pkg/sql/plan_opt.go:123: prepareUsingOptimizer()
github.com/cockroachdb/cockroach/pkg/sql/conn_executor_prepare.go:265: populatePrepared()
github.com/cockroachdb/cockroach/pkg/sql/conn_executor_prepare.go:207: func1()
github.com/cockroachdb/cockroach/pkg/sql/conn_executor_prepare.go:213: prepare()
github.com/cockroachdb/cockroach/pkg/sql/conn_executor_prepare.go:132: addPreparedStmt()
github.com/cockroachdb/cockroach/pkg/sql/conn_executor_exec.go:511: execStmtInOpenState()
github.com/cockroachdb/cockroach/pkg/sql/conn_executor_exec.go:120: execStmt()
github.com/cockroachdb/cockroach/pkg/sql/conn_executor.go:1502: func1()
github.com/cockroachdb/cockroach/pkg/sql/conn_executor.go:1504: execCmd()
github.com/cockroachdb/cockroach/pkg/sql/conn_executor.go:1429: run()
github.com/cockroachdb/cockroach/pkg/sql/conn_executor.go:483: ServeConn()
github.com/cockroachdb/cockroach/pkg/sql/pgwire/conn.go:625: func1()
runtime/asm_amd64.s:1374: goexit()

HINT: You have encountered an unexpected error.