Update React version check to support 18+ in Portal

[kmpeeduwee]

Fixes #0000

Checklist

• Includes tests

Changes proposed in this pull request:

• Update the Portal component to avoid using the old context API.
• Replace isReact18 function with isReact18OrHigher to ensure compatibility with React 19.
• Ensure that the new context API is used in React versions 18 and above, avoiding legacy context usage.

Reviewers should focus on:

• Correctness of the version-checking logic in isReact18OrHigher.
• Proper integration of the new context API in the Portal component.
• Compatibility of changes with React 19 and backwards compatibility with React 18.

[palantirtech]

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[changelog-app]

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• feature: A new feature of the service.
• improvement: An incremental improvement in the functionality or operation of the service.
• fix: Remedies the incorrect behaviour of a component of the service in a backwards-compatible way.
• break: Has the potential to break consumers of this service's API, inclusive of both Palantir services
  and external consumers of the service's API (e.g. customer-written software or integrations).
• deprecation: Advertises the intention to remove service functionality without any change to the
  operation of the service itself.
• manualTask: Requires the possibility of manual intervention (running a script, eyeballing configuration,
  performing database surgery, ...) at the time of upgrade for it to succeed.
• migration: A fully automatic upgrade migration task with no engineer input required.

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• ❗The break and manual task changelog types will result in a major release!
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• ✨ All others will result in a minor version release.

Type

• Feature
• Improvement
• Fix
• Break
• Deprecation
• Manual task
• Migration

Description

Update React version check to support 18+ in Portal

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