Export Reaction Interfaces

[khrj]

Summary

Accessing the "channel" type on event.item requires a type cast / type guard since multiple types exist. However, the types are not exported so this isn't possible.

Now:

app.event('reaction_added', async ({ event }) => {
        console.log(event.item.channel)
})

results in

Property 'channel' does not exist on type 'ReactionMessageItem | ReactionFileItem | ReactionFileCommentItem'.
  Property 'channel' does not exist on type 'ReactionFileItem'

After patch:

(preferred)

import { ReactionMessageItem } from '@slack/bolt' 
app.event('reaction_added', async ({ event }) => {
    if (reactionIsMessageItem(event.item)) {
        console.log(event.item.channel)
    }
})

function reactionIsMessageItem (reaction: ReactionMessageItem | ReactionFileItem | ReactionFileCommentItem): reaction is ReactionMessageItem {
    return !! (reaction as ReactionMessageItem).channel
}

or

import { ReactionMessageItem } from '@slack/bolt' 
app.event('reaction_added', async ({ event }) => {
    console.log(event.item.channel as ReactionMessageItem)
})

Requirements

• I've read and understood the Contributing Guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.

---

Fixes #765

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

Merging #776 (5d36e6d) into main (adff9a3) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #776   +/-   ##
=======================================
  Coverage   65.24%   65.24%           
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  Files          11       11           
  Lines        1082     1082           
  Branches      320      320           
=======================================
  Hits          706      706           
  Misses        317      317           
  Partials       59       59           

---

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[seratch]

Thanks for taking the time to make this PR! It seems that this pull request will fix #765

[khrj]

I've added a fixes note in the description

[stevengill]

Thanks for sending this PR!