Rollup merge of rust-lang#86136 - m-ou-se:proc-macro-open-close-span, r=m-ou-se

Stabilize span_open() and span_close().

This proposes to stabilize `Group::span_open()` and `Group::span_close()`.

These are part of the `proc_macro_span` feature gate tracked in rust-lang#54725

Most of the features gated behind `proc_macro_span` are about source location information (file path, line and column information), expansion information (parent()), source_text(), etc. Those are not ready for stabilizaiton. However, getting the span of the `(` and `)` separately instead of only of the entire `(...)` can be very useful in proc macros, and doesn't seem blocked on anything that all the other parts of `proc_macro_span` are blocked on. So, this renames the feature gate for those two functions to `proc_macro_group_span` and stabilizes them.

Author: JohnTitor

proc_macro/src/lib.rs

@@ -708,7 +708,7 @@ impl Group {
     /// pub fn span_open(&self) -> Span {
     ///                 ^
     /// ```
-    #[unstable(feature = "proc_macro_span", issue = "54725")]
+    #[stable(feature = "proc_macro_group_span", since = "1.55.0")]
     pub fn span_open(&self) -> Span {
         Span(self.0.span_open())
     }
@@ -719,7 +719,7 @@ impl Group {
     /// pub fn span_close(&self) -> Span {
     ///                        ^
     /// ```
-    #[unstable(feature = "proc_macro_span", issue = "54725")]
+    #[stable(feature = "proc_macro_group_span", since = "1.55.0")]
     pub fn span_close(&self) -> Span {
         Span(self.0.span_close())
     }