fix(ShardingManager): fix respawnAll not passing delay correctly

[kyranet]

Please describe the changes this PR makes and why it should be merged:

Shard#respawn takes delay, however, ShardingManager#respawnAll was passing shardDelay.

discord.js/src/sharding/Shard.js

Line 203 in 25b8491

async respawn({ delay = 500, timeout = 30_000 } = {}) {

Also fixes the return type being keyed with strings when it's keyed with numbers (shard IDs).

Status and versioning classification:

• Code changes have been tested against the Discord API, or there are no code changes
• I know how to update typings and have done so, or typings don't need updating