Show how to reference input event names correctly

[jenweber]

In earlier versions of Ember, inputs had a bug where certain event names could not be referenced as they were documented in the Guides, such as <Textarea @focus-in={{this.didFocusIn}} />. This has been fixed now! We should update the Guides to make sure they give the correct guidance. This issue is recommended for writers with some past technical writing experience or past contributions to Ember's documentation.

To-do:

• Try out the event passing like @focus-in in the latest stable version of Ember and confirm that it works
• Read over https://guides.emberjs.com/release/components/built-in-components/ and see which examples/explanations should be updated. It is possible that no changes are needed, since the source of the confusion was that the Guides said something should work that didn't, and now there's a bugfix. If that's the case, please comment on this issue.
• Feel free to open Issues for anything else you notice along the way that needs fixing
• Reach out to the learning team on #dev-ember-learning if you have questions.

For reference:

• Read past discussion here Input component does not accept documented event names emberjs/ember.js#18654
• Bugfix 1 [BUGFIX LTS] invoke methods correctly in TextSupport sendAction emberjs/ember.js#18997
• Bugfix 2 [BUGFIX LTS] invoke methods correctly in TextSupport sendAction emberjs/ember.js#19001

Note that there are still some complexities that are not bugs which remain, such as understanding how action, fn, and modifiers fit into this story. Those are out of scope for this issue, since our first step should always be to make sure that the Guides are correct. If you are on a roll and want to tackle that too, go for it! For ease of review, please do separate PRs if you choose to keep going.

[jenweber]

@ijlee2 is working on this issue.