chore: Replace eventBus with mitt.js [CW-3275]

[fayazara]

Replace the deprecated eventBus with mitt.js

Description

Since eventBus and it's respective methods are deprecated and removed from all future releases of vue, this was blocking us from migrating. This PR replaces eventBus with mitt. I have created a wrapper mitt.js to simulate the same old event names so it's backwards compatible, without making a lot of changes.

Fixes # (issue)

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality not to work as expected)
• This change requires a documentation update

How Has This Been Tested?

1. Made sure all the places we're listening to bus events are working as expected.
2. Respective specsf or the events from mitt.

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented on my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[linear]

CW-3275 Remove window.bus events and use mitt

[pranavrajs]

@fayazara A couple of thoughts.

1/ Can we remove the usage of window.bus from the code? I don't think it is good to use the same interface anymore.
2/ Please check the widget side code as well. It is not updated there.

[pranavrajs]

Please check the comment above.