Fix parsing usage for commands defined in CRLF (windows) files

Fixes nushell/nushell#13207

Before this commit, if the command was defined in a file that uses CR+LF
line endings, nu would fail to split the docblock into `usage` and
`extra_usage` (this also affected `std` that is baked into nu binary).

Now we first try to split the docblock by CRLF, and then by LF, thus
supporting both line ending styles in an OS-agnostic way.

crates/nu-protocol/src/engine/usage.rs

@@ -81,7 +81,9 @@ pub(super) fn build_usage(comment_lines: &[&[u8]]) -> (String, String) {
         usage.push_str(&comment_line);
     }
 
-    if let Some((brief_usage, extra_usage)) = usage.split_once("\n\n") {
+    if let Some((brief_usage, extra_usage)) = usage.split_once("\r\n\r\n") {
+        (brief_usage.to_string(), extra_usage.to_string())
+    } else if let Some((brief_usage, extra_usage)) = usage.split_once("\n\n") {
         (brief_usage.to_string(), extra_usage.to_string())
     } else {
         (usage, String::default())

tests/repl/test_parser.rs

@@ -261,6 +261,22 @@ fn commands_have_usage() -> TestResult {
     )
 }
 
+#[test]
+fn commands_from_crlf_source_have_short_usage() -> TestResult {
+    run_test_contains(
+        "# This is a test\r\n#\r\n# To see if I have cool usage\r\ndef foo [] {}\r\nscope commands | where name == foo | get usage.0",
+        "This is a test",
+    )
+}
+
+#[test]
+fn commands_from_crlf_source_have_extra_usage() -> TestResult {
+    run_test_contains(
+        "# This is a test\r\n#\r\n# To see if I have cool usage\r\ndef foo [] {}\r\nscope commands | where name == foo | get extra_usage.0",
+        "To see if I have cool usage",
+    )
+}
+
 #[test]
 fn equals_separates_long_flag() -> TestResult {
     run_test(