Resolve "Add externalization and fix regression in shortcuts helper modal"

What does this MR do?

This MR resolves #65530 (closed) by:

• Externalizing all of the text in the shortcuts help overlay
• Re-adding the correct missing classes so that sub-sections (issues, network, merge requests, wiki) appear when the overlay is shown on the correct page
• Enable the wiki sub-section when the shortcut overlay is shown on the wiki page

Notably, that last item was technically outside the original scope, but it seems like this would be incomplete if the wiki section still didn't work.

Does this MR meet the acceptance criteria?

I believe this does meet the acceptance criteria, but I'm not exactly sure where lines are drawn (for example, a regression test to confirm that these sections have the right classes and appear in the correct UIs?).

Conformity

• Changelog entry for user-facing changes, or community contribution. Check the link for other scenarios.
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content (https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/15063)

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• ~~Label as security and @ mention @gitlab-com/gl-security/appsec~~
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #65530 (closed)