Rollup merge of rust-lang#144903 - Kivooeo:panic_handler-is-not-begin, r=m-ou-se

Rename `begin_panic_handler` to `panic_handler`

Part of rust-lang#116005

Author: tgross35

std/src/panicking.rs

@@ -628,7 +628,7 @@ pub fn panicking() -> bool {
 /// Entry point of panics from the core crate (`panic_impl` lang item).
 #[cfg(not(any(test, doctest)))]
 #[panic_handler]
-pub fn begin_panic_handler(info: &core::panic::PanicInfo<'_>) -> ! {
+pub fn panic_handler(info: &core::panic::PanicInfo<'_>) -> ! {
     struct FormatStringPayload<'a> {
         inner: &'a core::panic::PanicMessage<'a>,
         string: Option<String>,