feat: make new unit outline design default and sidebar design fixes backport

[rpenido]

Description

Backport of #3034, #3055, #3056, and #3057

Supporting information

• Related to fix: course unit sidebar slot #3055 (comment)
• https://openedx.slack.com/archives/C06JG6RFE4V/p1780516019894209?thread_ts=1777989602.132059&cid=C06JG6RFE4V

Testing instructions

• Checkout this PR and run npm run build
• Check with the following env.config.jsx to see the behavior with insert/wrapping components:

import { PLUGIN_OPERATIONS, DIRECT_PLUGIN } from '@openedx/frontend-plugin-framework';

import { Card } from "@openedx/paragon"

const config = {
  pluginSlots: {
    'org.openedx.frontend.authoring.course_unit_sidebar.v2': {
      keepDefault: true,
      plugins: [
        {
          op: PLUGIN_OPERATIONS.Insert,
          widget: {
              id: 'course-unit-sidebar',
              priority: 1,
              type: DIRECT_PLUGIN,
              RenderWidget: () => <Card><Card.Header title="v2"/></Card>,
          },
        },
        {
            op: PLUGIN_OPERATIONS.Wrap,
            widgetId: 'default_contents',
            wrapper: ({component}) => (
                <div className="flex-fill d-flex overflow-hidden" style={{ border: 'thick dashed green' }}>
                    {component}
                </div>
            ),
        },
      ],
    },
    'org.openedx.frontend.authoring.course_outline_sidebar.v1': {
      keepDefault: true,
      plugins: [
        {
          op: PLUGIN_OPERATIONS.Insert,
          widget: {
              id: 'course-sidebar',
              priority: 1,
              type: DIRECT_PLUGIN,
              RenderWidget: () => <Card><Card.Header title="v2"/></Card>,
          },
        },
        {
            op: PLUGIN_OPERATIONS.Wrap,
            widgetId: 'default_contents',
            wrapper: ({component}) => (
                <div className="flex-fill d-flex overflow-hidden" style={{ border: 'thick dashed green' }}>
                    {component}
                </div>
            ),
        },
      ],
    },
  },
};

export default config;

Note: The flex classes in the wrapping divs are necessary so the content adapts to the remaining space correctly.

• Check that the sidebar on both Course Outline and Unit Outline has 100vh and occupies the whole left while scrolling.
• Resize your browser vertically and check if a scrollbar is shown inside the sidebar, and you can see the whole content.
• Try it with ENABLE_UNIT_PAGE_NEW_DESIGN set to both true and false.

Best Practices Checklist

We're trying to move away from some deprecated patterns in this codebase. Please
check if your PR meets these recommendations before asking for a review:

• Any new files are using TypeScript (.ts, .tsx).
• Avoid propTypes and defaultProps in any new or modified code.
• Tests should use the helpers in src/testUtils.tsx (specifically initializeMocks)
• Do not add new fields to the Redux state/store. Use React Context to share state among multiple components.
• Use React Query to load data from REST APIs. See any apiHooks.ts in this repo for examples.
• All new i18n messages in messages.ts files have a description for translators to use.
• Avoid using ../ in import paths. To import from parent folders, use @src, e.g. import { initializeMocks } from '@src/testUtils'; instead of from '../../../../testUtils'

[openedx-webhooks]

Thanks for the pull request, @rpenido!

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[navinkarkera]

@rpenido Looks good. I am assuming that the sidebar should not be sticky when ENABLE_UNIT_PAGE_NEW_DESIGN is false as this is the behavior in master too.

I just have one suggestion, can you use -x option when cherry picking these commits. It adds a nice reference link back to original commit.