feat(vue): add missing event emitter

[Kyri123]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build (npm run build) was run locally for affected output targets
• Tests (npm test) were run locally and passed
• Prettier (npm run prettier) was run locally and passed

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

• custom events will never emit in Vue

// will never fire!
function checkedChange(e) {
  console.log("checked!") 
}

<IxToggle @checkedChange="checkedChange" />

Issue URL: #382

What is the new behavior?

• Introduce the emitProps property to the defineContainer (an array for configuring event listeners on the Component, similar to the usage of @event() decorator in a web component).
• Revise the componentProps array and reposition the @Events() decorator under the emitProps section.

// will fire now
function checkedChange(e) {
  console.log("checked!")
}

<IxToggle @checkedChange="checkedChange" />

Does this introduce a breaking change?

• Yes
• No

Other information

[christian-bromann]

@Kyri123 any reasons for closing this? I know this PR has been around for a while but this doesn't mean we have rejected this patch.