[UX] add a center line indicator for settings sliders (like Audio Offset 0ms)

[rvnexe]

hi. it would be a better look to have a 0ms (center) indicator line.

Also applicable for:

• Gameplay/Menu cursor size = 1.0x
• UI scale = 1x
• Pen sensitivity = 1x
• Aspect ratio = 1.78 (tf why we use floats instead of 16:9?)
• Rotation = 90, 180, 270
• ... and maybe for other sliders to indicate default value? (especially osu!mania Scroll Speed = 8.0)

[rvnexe]

For Audio offset we can even set the origin of slider (the part where purple accent color starts) to the center too.

[peppy]

#38319

[rvnexe]

yooooooo