docs: Forms and mutations (#54314)

This PR is a larger change to documentation to make the following
updates:

- Deconstructs [Server
Actions](https://nextjs.org/docs/app/building-your-application/data-fetching/server-actions)
into "Forms and Mutations" and an API reference
- Removes content in place of future React API documentation pages
- Removes outdated [Building
Forms](https://nextjs.org/docs/pages/building-your-application/data-fetching/building-forms)
docs from the Pages Router and adds conditional content for both routes
in "Forms and Mutations"
- Adds TypeScript code blocks to API Routes page, recommends Route
Handlers for isomorphic signatures.
- Updates `revalidatePath` and `revalidateTag` docs to have a Server
Actions example.

---------

Co-authored-by: Delba de Oliveira <[email protected]>

docs/02-app/01-building-your-application/01-routing/10-route-handlers.mdx

@@ -170,7 +170,7 @@ export async function POST() {
 }
 ```
 
-> **Good to know**: Like API Routes, Route Handlers can be used for cases like handling form submissions. A new abstraction for [handling forms and mutations](/docs/app/building-your-application/data-fetching/server-actions) that integrates deeply with React is being worked on.
+> **Good to know**: Like API Routes, Route Handlers can be used for cases like handling form submissions. A new abstraction for [handling forms and mutations](/docs/app/building-your-application/data-fetching/forms-and-mutations) that integrates deeply with React is being worked on.
 
 ### Route Resolution
 

docs/02-app/01-building-your-application/02-data-fetching/01-fetching-caching-and-revalidating.mdx

@@ -17,7 +17,7 @@ There are four ways you can fetch data:
 
 Next.js extends the native [`fetch` Web API](https://developer.mozilla.org/en-US/docs/Web/API/Fetch_API) to allow you to configure the [caching](#caching-data) and [revalidating](#revalidating-data) behavior for each fetch request on the server. React extends `fetch` to automatically [memoize](/docs/app/building-your-application/data-fetching/patterns#fetching-data-where-its-needed) fetch requests while rendering a React component tree.
 
-You can use `fetch` with [`async`/`await` in Server Components](https://github.com/acdlite/rfcs/blob/first-class-promises/text/0000-first-class-support-for-promises.md), in [Route Handlers](/docs/app/building-your-application/routing/route-handlers), and in [Server Actions](/docs/app/building-your-application/data-fetching/server-actions).
+You can use `fetch` with [`async`/`await` in Server Components](https://github.com/acdlite/rfcs/blob/first-class-promises/text/0000-first-class-support-for-promises.md), in [Route Handlers](/docs/app/building-your-application/routing/route-handlers), and in [Server Actions](/docs/app/building-your-application/data-fetching/forms-and-mutations).
 
 For example:
 

docs/02-app/01-building-your-application/02-data-fetching/02-patterns.mdx

@@ -16,7 +16,7 @@ Whenever possible, we recommend fetching data on the server. This allows you to:
 - Reduce client-server [waterfalls](#parallel-and-sequential-data-fetching).
 - Depending on your region, data fetching can also happen closer to your data source, reducing latency and improving performance.
 
-You can fetch data on the server using Server Components, [Route Handlers](/docs/app/building-your-application/routing/route-handlers), and [Server Actions](/docs/app/building-your-application/data-fetching/server-actions).
+You can fetch data on the server using Server Components, [Route Handlers](/docs/app/building-your-application/routing/route-handlers), and [Server Actions](/docs/app/building-your-application/data-fetching/forms-and-mutations).
 
 ### Fetching Data Where It's Needed