use record separator \x1e for include_path (#8961)

# Description

This changes how the include paths are joined together so that it uses a
character that will work across platforms. `;` didn't work on Mac/Linux.
`:` didn't work in Windows. So, the record separator should work, which
is \x1e.

This goes hand-in-hand with
https://github.com/nushell/vscode-nushell-lang/pull/113.

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src/main.rs

@@ -141,7 +141,7 @@ fn main() -> Result<()> {
         let span = include_path.span;
         let vals: Vec<_> = include_path
             .item
-            .split(':')
+            .split('\x1e') // \x1e is the record separator character (a character that is unlikely to appear in a path)
             .map(|x| Value::String {
                 val: x.trim().to_string(),
                 span,