Navigation: expanded third-level menu chevron points sideways in RTL

In RTL the 3rd Level arrows of links points to the right instead of pointing up, which causes un matching the LTR behavior.

Problem/Motivation

In languages where the dir is RTL, the chevron on expanded third-level navigation items does not point up, but rotates to the sideway.

LTR Pic:

RTL Pic:

Steps to reproduce

1- Enable a language with RTL (for me it was arabic).
2- set the depth of one of the links block to 3 (In my case I made navigation_menu:admin into depth: 3 in navigation.block_layout).
3- Add a link under a second level link (for me it was under Structure › Display modes › Form modes).
4- Expand the links in the sidebar.

Proposed resolution

In core/modules/navigation/css/components/toolbar-menu.pcss.css, right in the style class of .toolbar-menu__chevron in rtl it is rotate: none. that style rotates the arrow to the right instead of up rotate: 270deg.

The compiled toolbar-menu.css has been regenerated to be:
[aria-expanded="true"] & {
rotate: -90deg;

[dir="rtl"] & {
rotate: 270deg;
}
}

Remaining tasks

- Fix the RTL chevron rotation for expanded third-level items: Done
- Manual testing in LTR and RTL: Done
- Open an MR and get CI passing: Done
- Review / RTBC

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet