Fix role index privilege panel resizing

[sophiec20]

Summary

Closes #232634

• Allows the index privilege panel to shrink inside the role editor flex layout.
• Enables Monaco automatic layout for the document-level security query editor.
• Adds a focused regression assertion for the DLS editor resize behavior.

Screenshot

Captured from a running local Kibana instance at /app/management/security/roles/edit/codex_dls_screenshot_role after resizing the viewport.

=Before=

=After=

Testing

• node scripts/jest x-pack/platform/plugins/shared/security/public/management/roles/edit_role/privileges/es/index_privilege_form.test.tsx
• node scripts/eslint x-pack/platform/plugins/shared/security/public/management/roles/edit_role/privileges/es/index_privilege_form.tsx x-pack/platform/plugins/shared/security/public/management/roles/edit_role/privileges/es/index_privilege_form.test.tsx

[infra-vault-gh-plugin-prod]

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