[For 2.20] Move ContainerRuntime class to internal scope

[markfields]

Description

Fixes AB#26794
See #23329

Stop exporting ContainerRuntime class under the /legacy path.

Breaking Changes

This is a breaking change since ContainerRuntime has been exported before. It's deprecated as of 2.12.0, and all known usages in partner codebases have been or are being removed.

[github-actions]

🔗 No broken links found! ✅

Your attention to detail is admirable.

linkcheck output

> fluid-framework-docs-site@0.0.0 ci:check-links /home/runner/work/FluidFramework/FluidFramework/docs
> start-server-and-test "npm run serve -- --no-open" 3000 check-links

1: starting server using command "npm run serve -- --no-open"
and when url "[ 'http://127.0.0.1:3000' ]" is responding with HTTP status code 200
running tests using command "npm run check-links"


> fluid-framework-docs-site@0.0.0 serve
> docusaurus serve --no-open

[SUCCESS] Serving "build" directory at: http://localhost:3000/

> fluid-framework-docs-site@0.0.0 check-links
> linkcheck http://localhost:3000 --skip-file skipped-urls.txt

Crawling...

Stats:
  170006 links
    1595 destination URLs
    1825 URLs ignored
       0 warnings
       0 errors