feat: add experimental option for sidebar auto-centering

[hajimemanila]

Description

This PR adds an experimental option to toggle the auto-centering behavior in the sidebar panel.

Following the recent change (commit e41d14d), the sidebar no longer auto-scrolls to the active tab. While this provides great operational stability for many, some power users with high tab counts still prefer the auto-centering navigation in the sidebar.

Key Changes

• New Setting: Added Auto-center active tab in sidebar under "Experimental Features" (disabled by default).
• Adaptive Logic: Refactored menulist-tab.ts to respect both the popup context and the user's preference.
• Backward Compatibility: Maintained the existing behavior for the toolbar popup.

Verification

• Verified that the sidebar stays stationary when the option is OFF.
• Verified that the sidebar auto-centers when the option is ON.
• Verified that the popup always auto-centers regardless of the setting.

Reference:
I shared some thoughts on why this toggle is beneficial for power users here:
[URL_OF_MY_COMMENT]