Dragging tabs should show an insertion target, not a replacement target

[joachim-n]

• VS Code Version: 1.54
• OS Version: MacOS 10.15.7

Steps to Reproduce:

1. Drag an editor tab to insert it between two other tabs.
2. The other tabs highlight when the mouse passes over it, as if to demonstrate that the tab I am dragging is going to go ONTO or REPLACE the highlighted tab. But that's not what will happen. The dragged tab will be INSERTED between two other tabs. Highlighting a tab like this is ambiguous: I can't tell whether the dragged tab will go to the left or the right of the highlighted tab when I drop it.

Instead, either an insertion mark should be shown to indicate the position where the dragged tab will go if I drop it, or the tabs should move to show the space where the dragged tab will go (as Firefox and Chrome currently behave).

Does this issue occur when all extensions are disabled?: Yes

[vscodebot]

(Experimental duplicate detection)
Thanks for submitting this issue. Please also check if it is already covered by an existing one, like:

• Drag and drop code between tabs (#44844)
• Drag out active tab to open it in new window (#117851)
• Close all/other tabs should close all saved tabs when some tabs are unsaved (#111973)
• Tab wrap - dragging a tab with wrapping could end up dragging the wrong tab (#115143)

[bpasero]

/duplicate #8544