fix: split shell exec pattern for terminal file picker on Windows

PowerShell's Exec uses `|` to separate alternative executable names, but
the file picker treated the whole string as a single glob, so pwsh.exe /
powershell.exe could not be selected. Split on `|` into separate patterns.

refactor: extract shell exec pattern split into a local variable

refactor: wrap shell exec pattern split across lines

Replaces the previously extracted local variable with a multi-line
expression for better readability.

Author: weiningwei

src/Views/Preferences.axaml.cs

@@ -341,7 +341,11 @@ private async void SelectShellOrTerminal(object _, RoutedEventArgs e)
             {
                 options = new FilePickerOpenOptions()
                 {
-                    FileTypeFilter = [new FilePickerFileType(shell.Name) { Patterns = [shell.Exec] }],
+                    FileTypeFilter = [new FilePickerFileType(shell.Name)
+                    {
+                        Patterns = shell.Exec.Split('|',
+                            StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries)
+                    }],
                     AllowMultiple = false,
                 };
             }