Rollup merge of #87993 - kornelski:try_reserve_stable, r=joshtriplett

Stabilize try_reserve

Stabilization PR for the [`try_reserve` feature](https://github.com/rust-lang/rust/issues/48043#issuecomment-898040475).

src/test/ui/closures/issue-87814-2.rs

@@ -1,5 +1,4 @@
 // check-pass
-#![feature(try_reserve)]
 
 fn main() {
     let mut schema_all: (Vec<String>, Vec<String>) = (vec![], vec![]);

src/test/ui/feature-gates/feature-gate-try_reserve.rs

@@ -1,4 +0,0 @@
-fn main() {
-    let v = Vec::new();
-    v.try_reserve(10); //~ ERROR: use of unstable library feature 'try_reserve'
-}

src/test/ui/feature-gates/feature-gate-try_reserve.stderr

@@ -1,12 +0,0 @@
-error[E0658]: use of unstable library feature 'try_reserve': new API
-  --> $DIR/feature-gate-try_reserve.rs:3:7
-   |
-LL |     v.try_reserve(10);
-   |       ^^^^^^^^^^^
-   |
-   = note: see issue #48043 <https://github.com/rust-lang/rust/issues/48043> for more information
-   = help: add `#![feature(try_reserve)]` to the crate attributes to enable
-
-error: aborting due to previous error
-
-For more information about this error, try `rustc --explain E0658`.