Fetch the execution context once in Array#each (#18610)

rb_yield() calls GET_EC() on every element, which on arm64 is an
out-of-line call to rb_current_ec() (RB_THREAD_CURRENT_EC_NOINLINE).
Hoist it out of the loop and use rb_ec_yield(), as ff831eb does
for Mutex#synchronize.

benchmark/loop_each.yml: 1.16x on arm64-darwin, 1.05x on aarch64-linux.

Author: sampokuokkanen

array.c

@@ -2786,8 +2786,9 @@ rb_ary_each(VALUE ary)
     long i;
     ary_verify(ary);
     RETURN_SIZED_ENUMERATOR(ary, 0, 0, ary_enum_length);
+    rb_execution_context_t *ec = GET_EC();
     for (i=0; i<RARRAY_LEN(ary); i++) {
-        rb_yield(RARRAY_AREF(ary, i));
+        rb_ec_yield(ec, RARRAY_AREF(ary, i));
     }
     return ary;
 }