Center tabbar in the NewFileDialog, this is the default in macOS #646

Job	Run time
acr-linux	4m 40s
acr-macos-m1	5m 19s
acr-macos-x64	9m 1s
acr-linux-r2git	6m 30s
meson (ubuntu-24.04, 3.8.x, true, default, default)	8m 18s
w64-meson	8m 50s
meson (ubuntu-22.04, 3.8.x, true, default, default)	6m 40s
meson (ubuntu-20.04, 3.8.x, true, default, default)	6m 5s
check_release	7s
release	0s
	55m 30s

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