Rollup merge of rust-lang#112790 - WaffleLapkin:syntactically, r=Nilstrieb

Syntactically accept `become` expressions (explicit tail calls experiment)

This adds `ast::ExprKind::Become`, implements parsing and properly gates the feature.

cc `@scottmcm`

Author: Noratrieb

clippy_utils/src/sugg.rs

@@ -211,6 +211,7 @@ impl<'a> Sugg<'a> {
             | ast::ExprKind::Path(..)
             | ast::ExprKind::Repeat(..)
             | ast::ExprKind::Ret(..)
+            | ast::ExprKind::Become(..)
             | ast::ExprKind::Yeet(..)
             | ast::ExprKind::FormatArgs(..)
             | ast::ExprKind::Struct(..)