hds-code-editor upgrade

[zamoore]

Description

• Swaps out usage of the code-mirror modifier with hds-code-editor
• Removes code-mirror modifier
• Removes CodeMirror 5 dependency

Testing & Reproduction steps

Ensure all code editors and code blocks function and look as intended.

Contributor Checklist

• Changelog Entry If this PR changes user-facing behavior, please generate and add a
  changelog entry using the make cl command.
• Testing Please add tests to cover any new functionality or to demonstrate bug fixes and
  ensure regressions will be caught.
• Documentation If the change impacts user-facing functionality such as the CLI, API, UI,
  and job configuration, please update the Nomad website documentation to reflect this. Refer to
  the website README for docs guidelines. Please also consider whether the
  change requires notes within the upgrade guide.

Reviewer Checklist

• Backport Labels Please add the correct backport labels as described by the internal
  backporting document.
• Commit Type Ensure the correct merge method is selected which should be "squash and merge"
  in the majority of situations. The main exceptions are long-lived feature branches or merges where
  history should be preserved.
• Enterprise PRs If this is an enterprise only PR, please add any required changelog entry
  within the public repository.

[KristinLBradley]

@zamoore To keep it on your radar, there are some Percy diffs resulting from refactoring of the PageHeader component bottom spacing included in HDS 4.18.1: #25579

This spacing will have to be replaced with a custom style or similar.