Rollup merge of rust-lang#136591 - GuillaumeGomez:expr-to-string, r=Urgau

Add `rustc_hir_pretty::expr_to_string` function

It'll allow me to work on a new rustdoc feature. :)

r? `@Urgau`

Author: workingjubilee

Diff for: compiler/rustc_hir_pretty/src/lib.rs

@@ -321,6 +321,10 @@ pub fn pat_to_string(ann: &dyn PpAnn, pat: &hir::Pat<'_>) -> String {
     to_string(ann, |s| s.print_pat(pat))
 }
 
+pub fn expr_to_string(ann: &dyn PpAnn, pat: &hir::Expr<'_>) -> String {
+    to_string(ann, |s| s.print_expr(pat))
+}
+
 impl<'a> State<'a> {
     fn bclose_maybe_open(&mut self, span: rustc_span::Span, close_box: bool) {
         self.maybe_print_comment(span.hi());