refactor: declare methods in methods instead of created

[malangfox]

Issue

#770

Details

This changes getPanels and getVirtualPanels to be initialized in methods instead of created.
In some cases, such a warning appears because the methods declared in created are not recognized.

[coveralls]

Coverage: 79.337% (+0.1%) from 79.233% when pulling 15dae40 on malangfox:refactor-vue3-methods into 761aa92 on naver:master.

[WoodNeck]

Have you been able to test this fix works in both our demo & Vite?
I remember that was defined like that because getCurrentInstance returned the wrong result when used in methods I guess.

I don't know if it was an issue with a specific version of Vue, but please at least test whether it works fine with the latest version of Vue.

[daybrush]

LGTM

@malangfox
Check if this is the case in vue2 as well.

[daybrush]

LGTM