#422 Update React docs to v19

[kristersd]

Updated React documentation to version 19.

Extra notes:

• Allow trailing dot (.) for the search term.
• Replace double empty-blank lines for the content to single line.

Closes #422.

[what-the-diff]

PR Summary

• Change in search key extraction
  We updated the rule for extracting search keys. Now it excludes periods in the keys to improve the search experience.

• Improvement in introduction content extraction
  The way we extract introduction content has been modified. Now, it replaces multiple line breaks with just one, making the processed content cleaner.

• Addition of new entries in React documentation list
  Our software now recognizes newer react features such as react/act and react/useActionState.

• Removal of outdated entries from React documentation list
  We have cleaned up our list of react features. Outdated features not in use anymore like react/createFactory, react/use-client, and react/use-server have been removed.

• Inclusion of react-dom utilities in React documentation list
  Our system now understands several new react-dom utilities, improving the way it handles react related code. Some of these are react-dom/flushSync and react-dom/preload.