Fix animatedPosition initialization logic

[kliakhovskii-brex]

Motivation

Tldr - fixing the issue described here:
#2582

This initializes the animatedPosition with the right value if animateOnMount is disabled.

This avoids two issues:

• Fixes issue with animation still playing if Layout is treated to be ready right away (e.g. no handle component and known size)
• Fixes first frame rendering in case when Layout is not ready (e.g. so the position is open right away rather than close -> open jump)