[useScrollLock] Fix jump with scroll-behavior style

[atomiks]

Fixes #1340

Unfortunately body { scroll-behavior: smooth } still jumps (when I tried to add the same technique), although it fixes the html case.

A couple of options are possible:

• Just warn that scroll-behavior should be put on html instead of body. This isn't going to work nicely if Base UI is used as an extension since they can't control third party sites.
• Fallback to the react-aria hook (+ maybe warn still). This isn't straightforward due to the fact the react-aria lock is disabled on open not mounted, so a position: fixed element (e.g. dialog) shifts while closing if it has an exit animation when the body has inset scrollbars. A bunch of extra code is necessary to ensure this works correctly

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