Add a default state attribute for target elements

[fredmef]

Is your feature request related to a problem? Please describe.
I'm always frustrated when I need to wait the initialization of the triggers to have the default state of the target elements. This behavior creates some glitchs or layout shifting which provides a bad user experience.

Describe the solution you'd like
Can it be possible to have an attribute like data-toggle-is-active (eg: data-toggle-target-is-active) for the target elements to avoid waiting initialization to have the default state for target elements ?

Describe alternatives you've considered
None.

Additional context
None.

[aaronstezycki]

I think a slightly better approach, would be to use an "active" class already set in the html which can then be toggled by clicking a trigger. I.e Add .is-active to both the trigger and the "active" target. Then on initialisation the js has the smarts to know that if the trigger and target are "active" don't trigger the active state, but allow for further toggling i.e if it's a tabs/accordion component etc. I want to provide a basic test case, but I don't have the time atm.

[aaronstezycki]

... but yeah, currently this can create large layoutshifts on load and needs fixing asap I think.