fix: assert channel types in message actions

[SpaceEEC]

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

This PR ensures that message related actions take place in a channel that is supported to avoid throwing an unhandled exceptions. (Read: text in voice, also future-proofing)

Changed actions:

• MessageCreate
• MessageDelete
• MessageReactionAdd
• MessageReactionRemove
• MessageReactionRemoveAll
• MessageReactionRemoveEmoji
• MessageUpdate
• TypingStart

The reaction actions previously were ensuring that the action was not taking place in a voice channel (as per type) and the typing start action in a text channel (as per type).

I went with Channel#isText since it seems to be the less error-prone method to check whether messages can be accessed in said channel, since it's just return 'messages' in this.

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

[ImRodry]

Voice channels will soon have messages though, are you sure you wanna do this?

[SpaceEEC]

Yes, I am.