[🔧 esl-panel-group]: internal check for `has-opened` is inconsitent

[ala-n]

As a consumer/architect, I want to have consistent and clear conditions for esl-panel-group component behavior.

Current state:

• initial has-opened state = this.$activePanels.length > 0 which is logical
• on panels state change, it is updated with the event panel state this.toggleAttribute('has-opened', panel.open); which is inconsistent

Expected behavior:

• this.$activePanels.length > 0 - the only criteria to set has-opened state

Scope

• Cover has-opened marker state with unit tests
• Make behavior consistent

Originally proposed by @andreybelous

[ala-n]

:tada: This issue has been resolved in version 5.0.0-beta.1 :tada:

The release is available on:

• npm package (@beta dist-tag)
• GitHub release

Your semantic-release bot :package::rocket:

[ala-n]

:tada: This issue has been resolved in version 4.15.0 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot :package::rocket: