Introduce grow-parent class for widgets (#6194)

Only some widgets actually want to grow. Flex makes this difficult. This
PR sets up a `widget-expands` class that widgets can use to indicate
that they want to dynamically grow and applies it to the textarea widget
<img width="709" height="860" alt="image"
src="https://github.com/user-attachments/assets/721d99e5-5939-4531-91b5-1cda69d4e8ed"
/>


There's a potential alternative avenue with using `flex-shrink` instead
of `flex-grow`, and using `min-content` for `calculateIntrinsicSize`,
but I've been poking around with that for a while with no success.

┆Issue is synchronized with this [Notion
page](https://www.notion.so/PR-6194-Introduce-grow-parent-class-for-widgets-2946d73d3650812f9d03c305ab04e212)
by [Unito](https://www.unito.io)

---------

Co-authored-by: github-actions <[email protected]>

Author: AustinMroz

browser_tests/tests/vueNodes/interactions/links/linkInteraction.spec.ts-snapshots/vue-node-dragging-link-chromium-linux.png

@@ -19,7 +19,7 @@
     <div
       v-for="(widget, index) in processedWidgets"
       :key="`widget-${index}-${widget.name}`"
-      class="group flex flex-1 items-stretch"
+      class="group flex items-stretch has-[.widget-expands]:flex-1"
     >
       <!-- Widget Input Slot Dot -->