Refactor(createFlash): call original from deprecated

What does this MR do?

This MR shifts the implementation of the deprecatedCreateFlash to call createFlash instead. This will make it easier for us to do incremental updates to move away from calling deprecatedCreateFlash to calling createFlash directly.

This MR is preparation for following MRs like this: !55549 (merged)

What is the difference:

Functionally, there is not much difference between createFlash and deprecatedCreateFlash. The former reports to Sentry, uses gl-display-block, instead of display: 'block', and does not overwrite existing messages. Other than that, they work the same.

Screenshots (strongly suggested)

Before	After

No visual changes.

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because there are no user-facing changes.
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

Availability and Testing

Pick any page you are familiar with and add these two lines to see it working:

import { deprecatedCreateFlash } from '~/flash';
deprecatedCreateFlash('An error occurred');

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• [-] Informed Infrastructure department of a default or new setting change, if applicable per definition of done

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

Related to #3895 (closed)