Auto merge of #117825 - fee1-dead-contrib:corefx, r=petrochenkov

Reenable effects in libcore

With #116670, #117531, and #117171, I think we would be comfortable with re-enabling the effects feature for more testing in libcore.

r? `@oli-obk`
cc `@fmease`
cc #110395

library/core/src/lib.rs

@@ -219,6 +219,7 @@
 #![feature(doc_cfg)]
 #![feature(doc_cfg_hide)]
 #![feature(doc_notable_trait)]
+#![feature(effects)]
 #![feature(exhaustive_patterns)]
 #![feature(extern_types)]
 #![feature(fundamental)]