Enable const tests for bool methods

This change re-enables the const tests for bool::then_some and bool::then
that were previously disabled with a FIXME comment referencing issue 110395.

The tests verify that these methods work correctly in const contexts, which
is important for compile-time evaluation. These tests check that both the
eager evaluation variant (then_some) and lazy evaluation variant (then)
can be used to create constant Option values at compile time.

Tests added:
- Const evaluation of false.then_some(0) returning None
- Const evaluation of true.then_some(0) returning Some(0)
- Const evaluation of false.then(zero) returning None
- Const evaluation of true.then(zero) returning Some(0)

Author: dollaransh17

library/coretests/tests/bool.rs

@@ -89,7 +89,6 @@ fn test_bool_to_option() {
     assert_eq!(false.then(|| 0), None);
     assert_eq!(true.then(|| 0), Some(0));
 
-    /* FIXME(#110395)
     const fn zero() -> i32 {
         0
     }
@@ -103,7 +102,6 @@ fn test_bool_to_option() {
     assert_eq!(B, Some(0));
     assert_eq!(C, None);
     assert_eq!(D, Some(0));
-    */
 }
 
 #[test]