Add logical xor operator (#7242)

We already have the binary `bit-xor` and the shortcircuiting logical
`or`(`||`) and `and`(`&&`).
This introduces `xor` as a compact form for both brevity and clarity.
You can express the operation through `not`/`and`/`or` with a slight
risk of introducing bugs through typos.

Operator precedence

`and` > `xor` > `or`

Added logic and precedence tests.

crates/nu-parser/src/parser.rs

@@ -4502,6 +4502,7 @@ pub fn parse_operator(
         b"ends-with" => Operator::Comparison(Comparison::EndsWith),
         b"&&" | b"and" => Operator::Boolean(Boolean::And),
         b"||" | b"or" => Operator::Boolean(Boolean::Or),
+        b"xor" => Operator::Boolean(Boolean::Xor),
         b"**" => Operator::Math(Math::Pow),
         _ => {
             return (

crates/nu-parser/src/type_check.rs

@@ -244,7 +244,9 @@ pub fn math_result_type(
                     )
                 }
             },
-            Operator::Boolean(Boolean::And) | Operator::Boolean(Boolean::Or) => {
+            Operator::Boolean(Boolean::And)
+            | Operator::Boolean(Boolean::Or)
+            | Operator::Boolean(Boolean::Xor) => {
                 match (&lhs.ty, &rhs.ty) {
                     (Type::Bool, Type::Bool) => (Type::Bool, None),