LangChain Integration Docs: Find information faster with revamped pages & API references

LangChain has over 1,000 integrations for LLMs, vector stores, tools, document loaders, and more, which were recently revamped to have standardized content, new index pages with streamlined search, and improved API references. The goal of these changes is to help developers quickly identify what an integration can do and how to use it, by providing better documentation that is more modern, user-friendly, and evergreen. The updates include a "Features" table on each component's page, which highlights the features supported by each integration.