refactor(api-markdown-documenter): Add and use a ValidApiItemKind type alias which excludes the None value

[Josmithr]

No valid ApiItem will have kind "None". There are a number of places where we are forced to assert that an item's kind is not "None" to make checks exhaustive, and there are other places where we probably should have been.

This PR adds a helper type alias and a helper function to encapsulate the validity checking.

Copilot reviewed 5 out of 9 changed files in this pull request and generated no comments.

Files not reviewed (4)

• tools/api-markdown-documenter/src/api-item-transforms/ApiItemTransformUtilities.ts: Evaluated as low risk
• tools/api-markdown-documenter/src/api-item-transforms/TransformApiItem.ts: Evaluated as low risk
• tools/api-markdown-documenter/src/api-item-transforms/configuration/DocumentationSuiteOptions.ts: Evaluated as low risk
• tools/api-markdown-documenter/src/api-item-transforms/default-implementations/TransformApiClass.ts: Evaluated as low risk

Comments suppressed due to low confidence (1)

tools/api-markdown-documenter/src/utilities/ApiItemUtilities.ts:58

• The error message should include more context about where the error occurred. Consider updating it to: Encountered an API item with kind "None" in getApiItemKind function: "${apiItem.displayName}".

throw new Error(`Encountered an API item with kind "None": "${apiItem.displayName}".`);

[Josmithr]

This was a bug. Should have been Exclude and not Omit.

[Josmithr]

Handling was not exhaustive, revealed by fixing ApiMemberKind

[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:
  170138 links
    1596 destination URLs
    1825 URLs ignored
       0 warnings
       0 errors