add: isSlashCommand typeGuard

src/types/channels/threads/is_slash_command.ts

@@ -0,0 +1,7 @@
+import { Interaction, SlashCommandInteraction } from "../../interactions/interaction.ts";
+import { DiscordInteractionTypes } from "../../interactions/interaction_types.ts";
+
+/** A type guard function to tell if it is a slash command interaction */
+export function isSlashCommand(interaction: Interaction): interaction is SlashCommandInteraction {
+  return interaction.type === DiscordInteractionTypes.ApplicationCommand;
+}