Rollup merge of rust-lang#79211 - yoshuawuyts:future-doc-alias, r=Mark-Simulacrum

Add the "async" and "promise" doc aliases to `core::future::Future`

Adds the "async" and "promise" doc aliases to `core::future::Future`. This enables people who search for "async" or "promise" to find `Future`, which is Rust's core primitive for async programming. Thanks!

Author: JohnTitor

library/std/src/keyword_docs.rs

@@ -2196,6 +2196,7 @@ mod where_keyword {}
 
 // 2018 Edition keywords
 
+#[doc(alias = "promise")]
 #[doc(keyword = "async")]
 //
 /// Return a [`Future`] instead of blocking the current thread.