docs(angular, core): change link from slack to discord (#27519)

Issue number: N/A

[The Stencil team has moved their community from Slack to
Discord](https://twitter.com/stenciljs/status/1658561079767887873).

---------

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issue. -->

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## What is the current behavior?
<!-- Please describe the current behavior that you are modifying. -->
There is a link to the Slack.

## What is the new behavior?
<!-- Please describe the behavior or changes that are being added by
this PR. -->

- There is a link to the Discord.

## Does this introduce a breaking change?

- [ ] Yes
- [x] No

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and migration path for existing applications below. -->


## Other information

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screenshots of how the component looks before and after the change. -->

angular/README.md

@@ -7,10 +7,10 @@ Ionic Angular specific building blocks on top of [@ionic/core](https://www.npmjs
 
 * [Ionic Core Components](https://www.npmjs.com/package/@ionic/core)
 * [Ionic Documentation](https://ionicframework.com/docs/)
+* [Ionic Discord](https://ionic.link/discord)
 * [Ionic Forum](https://forum.ionicframework.com/)
 * [Ionicons](http://ionicons.com/)
 * [Stencil](https://stenciljs.com/)
-* [Stencil Worldwide Slack](https://stencil-worldwide.slack.com/)
 * [Capacitor](https://capacitor.ionicframework.com/)
 
 

core/README.md

@@ -101,10 +101,10 @@ const showModal = async () => {
 ## Related
 
 * [Ionic Documentation](https://ionicframework.com/docs/)
+* [Ionic Discord](https://ionic.link/discord)
 * [Ionic Forum](https://forum.ionicframework.com/)
 * [Ionicons](http://ionicons.com/)
 * [Stencil](https://stenciljs.com/)
-* [Stencil Worldwide Slack](https://stencil-worldwide.slack.com/)
 * [Capacitor](https://capacitor.ionicframework.com/)