Rollup merge of rust-lang#102144 - chriss0612:const_convert_control_flow, r=scottmcm

Extend const_convert with const {FormResidual, Try} for ControlFlow.

Very small change so I just used the existing `const_convert` feature flag.  rust-lang#88674
Newly const API:
```
impl<B, C> const ops::Try for ControlFlow<B, C>;
impl<B, C> const ops::FromResidual for ControlFlow<B, C>;
```

`@usbalbin` I hope it is ok that I added to your feature.

Author: matthiaskrgr

library/core/src/ops/control_flow.rs

@@ -95,7 +95,8 @@ pub enum ControlFlow<B, C = ()> {
 }
 
 #[unstable(feature = "try_trait_v2", issue = "84277")]
-impl<B, C> ops::Try for ControlFlow<B, C> {
+#[rustc_const_unstable(feature = "const_convert", issue = "88674")]
+impl<B, C> const ops::Try for ControlFlow<B, C> {
     type Output = C;
     type Residual = ControlFlow<B, convert::Infallible>;
 
@@ -114,7 +115,8 @@ impl<B, C> ops::Try for ControlFlow<B, C> {
 }
 
 #[unstable(feature = "try_trait_v2", issue = "84277")]
-impl<B, C> ops::FromResidual for ControlFlow<B, C> {
+#[rustc_const_unstable(feature = "const_convert", issue = "88674")]
+impl<B, C> const ops::FromResidual for ControlFlow<B, C> {
     #[inline]
     fn from_residual(residual: ControlFlow<B, convert::Infallible>) -> Self {
         match residual {