Image Compare Block: invert the for RTL sites (Arabic)

A user [in the Jetpack forum](https://wordpress.org/support/topic/jetpack-image-compare-is-inverse-in-rtl-site/) would like to have the image move control sliding on the same way the RTL (Arabic) reads, which is from left to right.

At the moment, the slide moves only from the right to left, so in RTL sites this might cause some confusion:


Start by locating the Image Compare Block implementation and reviewing the linked Jetpack forum report and screenshot. Verify how the control currently moves on RTL sites, then confirm the block follows the requested RTL reading direction without changing its behavior for other sites.

Written by the indexing model from the issue text.