Internal issue 3134 - Vertical IcDivider should expose `flexItem`-like prop

Nobody has claimed this yet.

h3. Summary

Add a {{flexItem}}-like prop (from MUI’s Divider API) to make vertical dividers behave as expected in flex containers.

h3. 💬 Description

An IcDivider in the vertical configuration (i.e. {{}}) will not display as expected if the parent element is a flexbox without an explicit height set. This is also the same behaviour observed with MUI’s React Divider component by default. However, MUI’s Divider API exposes a {{flexItem}} prop:

{quote}If {{true}}, a vertical divider will have the correct height when used in flex container. (By default, a vertical divider will have a calculated height of {{0px}} if it is the child of a flex container.){quote}

IcDivider should ideally expose a similar prop.

h3. 💰 Use value

This will make the IcDivider easier/more intuitive to use in the vertical configuration, as currently a flexbox parent with no explicit height (i.e. height controlled intrinsically) will result in the IcDivider not displaying.

h3. 📝 Acceptance Criteria

_Given I have a flexbox with no explicit height set_
_When I add an IcDivider in the vertical orientation (perhaps with a prop like_ {{flexItem}} _set to_ {{true}}_)_
_Then the IcDivider should render_

h3. ✏ Designs

N/A

h3. 🧾 Guidance

MUI Divider API docs: [https://mui.com/material-ui/api/divider/#:~:text=flexItem,-boolfalse|https://mui.com/material-ui/api/divider/#:~:text=flexItem,-boolfalse]

MUI Divider source: [https://github.com/mui/material-ui/blob/master/packages/mui-material/src/Divider/Divider.js|https://github.com/mui/material-ui/blob/master/packages/mui-material/src/Divider/Divider.js]

h3. 🚨 Urgency (low, medium or high)

Medium

h3. Additional info

N/A

Start at the IcDivider component entry point and inspect how its vertical orientation sizes itself inside a flex container. Compare the relevant behavior with the linked MUI Divider source, then verify the acceptance scenario: a vertical IcDivider in a flex parent without an explicit height renders correctly when the new prop is enabled.

Written by the indexing model from the issue text.