fix(TextBasedChannel): return the cached message instead of clone it

[StefansArya]

Please describe the changes this PR makes and why it should be merged:
This probably will also fix #6348 and #6763 about the .deleted flags that does never get updated. Their code example wasn't using setTimeout and makes it looks like a race condition. But actually I also encounter about this problem and found that the returned object from textChannel.send is cloned from the original object, while the cache only stored the original message object. The .deleted flag on cached message will get updated, but the cloned message will never get updated because the object property is copied by using Object.assign from the ._clone method.

The code sample about this fix:

let message = await textChannel.send({content: "lalala"}); // Send message
await message.delete(); // Delete it

console.log("Message deleted 1:", message.deleted);

setTimeout(function() {
    console.log("Message deleted 2:", message.deleted);
}, 2000);

Result:

// Before the fix
Message deleted 1: false
Message deleted 2: false // This still false, but the cache already updated to true

// After this fix
Message deleted 1: true // Some time this return false for me, but mostly it return true
Message deleted 2: true

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