Fix on latest nightly

[PacificViking]

Fixes #113 on latest nightly tested on Linux.

I used MrOtherGuy's inspiration and added part name to the html:slot so I can select it. This fixes all issues I encountered.

[adisor19]

Looks like Firefox 141 broke multiple rows of tabs again :/

[PacificViking]

I have pushed a fix that makes it "work" on my newest nightly. (they just renamed the container that contains all the tabs again lol)

It breaks every drag and drop movement on a tab except physically moving it or moving it to another window (e.g. pinning it or putting into groups). This is because the calculations for where to put a tab once dragged and dropped is in the same function as all the other things, so I just overrode it with numirias's function.

Pinned tabs now also look ugly because I think there's just a new DOM object for all the pinned tabs now and I don't want to bother with it.

The drag and drop to move still works under the hood but there's a displacement going on whenever I do it that I have no clue about. Just pretend the tabs are still in the right place. (I'll still try to fix this over time)

Hey, at least the basic idea of "multi tier tabs" is fixed.