Menu/MenuItem - should support drill-[up/out] icon/layout in menu list

re: https://github.com/patternfly/patternfly-react/issues/9587 and this issue to make the same update in core https://github.com/patternfly/patternfly/issues/5950. Not sure if this is a breaking change or not, probably depends on how we go about implementing it.

In the drilldown with breadcrumb menu examples, in the breadcrumb dropdown, we have items that present (and seem to function) as drill-[up/out] items with a back arrow at the start of the item, and clicking on the item takes you up a level in the breadcrumb hierarchy. However, our component doesn't support this layout - our examples are using a user-supplied icon passed as the icon prop - https://github.com/patternfly/patternfly-react/blob/e27aac2f35e0a8bb16fa5397eb5ef841b3ecc578/packages/react-core/src/components/Menu/examples/MenuWithDrilldownBreadcrumbs.tsx#L130-L138

Some issues with this are:

1. It doesn't work by default in RTL since we can't predictably target and mirror/flip that menu item icon for the user since that could be a non-directional icon or they may have opted for some other type of directional icon there that shouldn't be flipped.
2. Since it's a user supplied icon, there is the possibility for inconsistency
3. I could be wrong, but I don't know if a user could pass an actual icon to any of those items since the prop is being used for the back arrow.

We have a direction="up" prop that puts the correct icon container and icon on a drill-up/out icon and works in RTL, but that is specific to the top/first item in a drilled-in drilldown menu. The prop applies other logic to that item that isn't appropriate for use in the breadcrumb items, so we can't use that prop there. https://github.com/patternfly/patternfly-react/blob/e27aac2f35e0a8bb16fa5397eb5ef841b3ecc578/packages/react-core/src/components/Menu/MenuItem.tsx#L366-L370

Ideally we could do something like update the direction prop so it could be used in these breadcrumb menu items or maybe introduce some new kind of prop for an item that indicates clicking it does some kind of "back" action and it just borrows the way direction="up" includes the icon in the item.

Jira Issue: PF-116

從 packages/react-core/src/components/Menu/MenuItem.tsx 開始，特別查看現有的 direction="up" 處理，以及 issue 中連結的 MenuWithDrilldownBreadcrumbs.tsx 範例。將目前的 breadcrumb dropdown 行為與 core issue 和 RTL 預期進行比較。完成的標準是：breadcrumb drill-up/out 項目具有一致且適應方向的版面配置，不依賴使用者提供的返回圖示。