Expose flags on MessageEdit so you can suppress embeds on other messages

[nixxquality]

This pull request exposes the flags member of the MessageEdit struct so you can suppress embeds on other people's messages.

Other users can only edit flags and only if they have the MANAGE_MESSAGES permission in the corresponding channel.
https://discord.com/developers/docs/resources/channel#edit-message

I've tested it and it works with the following code:

original, err := s.ChannelMessage("290610944458096642", "867522047768133632")
edit := discordgo.NewMessageEdit("290610944458096642", "867522047768133632")
edit.Flags = original.Flags | discordgo.MessageFlagsSuppressEmbeds
msg, err := s.ChannelMessageEditComplex(edit)

Additionally, I wanted to include a convenience function for suppressing embeds on a message like so:

// SuppressEmbeds is a convenience function that sets the
// SUPPRESS_EMBEDS flag on the message.
func (m *MessageEdit) SuppressEmbeds() *MessageEdit {
	m.Flags = MessageFlagsSuppressEmbeds
	return m
}

However, that wouldn't work.

When specifying flags, ensure to include all previously set flags/bits in addition to ones that you are modifying.
https://discord.com/developers/docs/resources/channel#edit-message

Since the MessageEdit struct knows nothing about the message it's editing and it's not connected to a session, I'm not sure how you would like to handle this.

Should it not be included?

Should the MessageEdit include a reference to the Session that created it?

I also changed two more things. First, I noticed a typo in the enum so I marked that member as deprecated (not sure if that works?) and included a fixed one with the same value.

I also had to make Components omitempty on the MessageEdit struct or Discord would give an error about "Cannot edit a message authored by another user"

[FedorLap2006]

I think it would be best to just put it right after the corrected constant.

[nixxquality]

The reason I put it separate was because of a gofmt error in the previous build

0.06s$ diff <(gofmt -d .) <(echo -n)
1,14d0
< diff -u message.go.orig message.go
< --- message.go.orig	2021-07-22 08:05:45.890441692 +0000
< +++ message.go	2021-07-22 08:05:45.890441692 +0000
< @@ -172,8 +172,8 @@
<  
<  // Valid MessageFlags values
<  const (
< -	MessageFlagsCrossPosted          MessageFlags = 1 << 0
< -	MessageFlagsIsCrossPosted        MessageFlags = 1 << 1
< +	MessageFlagsCrossPosted   MessageFlags = 1 << 0
< +	MessageFlagsIsCrossPosted MessageFlags = 1 << 1
<  	// Deprecated: use MessageFlagsSuppressEmbeds
<  	MessageFlagsSupressEmbeds        MessageFlags = 1 << 2
<  	MessageFlagsSuppressEmbeds       MessageFlags = 1 << 2
The command "diff <(gofmt -d .) <(echo -n)" exited with 1.

Between messing up the spacing or extracting it to a separate section I chose the latter.

[FedorLap2006]

Just put it at the end of the section, like that

const (
   ...
   // TODO: remove when compatibility is not required
   MessageFlagsSupressEmbeds       MessageFlags = 1 << 2
)

[FedorLap2006]

This was intentional, to allow users to remove components from messages.
Also it would be probably better to move this into a separate PR.

[nixxquality]

I had to add this to make it work. Before I added it, Discord would give an error about "Cannot edit a message authored by another user"

This seems to be mutually exclusive with your current requirements, so I don't know what to do about that.

[FedorLap2006]

While it's related to SuppressEmbeds flag, the issue existed before, so I think it would be better to resolve this in a separate PR.

[FedorLap2006]

Sorry it took a long time

[FedorLap2006]

Also, please note the conflicts

[FedorLap2006]

I've made a couple of changes myself, to speed up the process.
But thanks for the contribution!