_prepareAvatars() {
      this._colorIndex = 0;
      this.items.forEach((avatar, index) => {
        const colorIndex = this._getNextBackgroundColor();
        avatar.interactive = !this._isGroup;
        if (!avatar.getAttribute("_color-scheme")) {
          // AvatarGroup respects colors set to ui5-avatar
          avatar.setAttribute("_color-scheme", _AvatarColorScheme.default[`Accent${colorIndex}`]);
        }
        // last avatar should not be offset as it breaks the container width and focus styles are no set correctly
        if (index !== this._itemsCount - 1 || this._customOverflowButton) {
          // based on RTL the browser automatically sets left or right margin to avatars
          avatar.style.marginInlineEnd = offsets[avatar._effectiveSize][this.type];
        }
      });
    }
Modifies avatars to the needs of avatar group properties. Respects already set size and background color.
Set the margins (offsets) based on RTL/LTR.
@private