Test: new tab layout option

[bpasero]

• win @dbaeumer
• mac @roblourens
• linux @kieferrm

Refs: #15048
Complexity: 3

A new setting workbench.editor.tabSizing is added to control the behaviour of tabs when the size of the editor group is too little to show all tabs. The new behaviour can be enabled by setting this option to shrink.

Verify:

• if space is enough, tabs show fully with the editor name
• tabs will start to shrink and show a "..." when space gets little
• you still get a scrollbar when tabs shrink enough to their min size
• this works with icons enabled or not
• this works when tab close button is on the left hand side or disabled (via workbench.editor.tabCloseButton)