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

[weiningwei]

On Windows, the shell/terminal file picker in Preferences could not display pwsh.exe / powershell.exe when the user tried to manually select the PowerShell executable.

Root cause

ShellOrTerminal.Exec for PowerShell is "pwsh.exe|powershell.exe", using | as a separator for alternative executable names. The file picker (SelectShellOrTerminal in src/Views/Preferences.axaml.cs) passed the entire string as a single glob pattern to FilePickerFileType.Patterns:

Patterns = [shell.Exec]

Avalonia's Win32 implementation joins the patterns with ; and hands the result to the native file dialog, which treats | as a literal character rather than an alternative separator. Since no file is literally named pwsh.exe|powershell.exe, the dialog showed nothing in the target directory.

The other Windows terminals (bash.exe, cmd.exe, wt.exe) use a single executable name and are unaffected.

Fix

Split Exec on | so each alternative becomes its own pattern entry. For PowerShell this produces ["pwsh.exe", "powershell.exe"], which the Win32 dialog matches as pwsh.exe;powershell.exe.

Patterns = shell.Exec.Split('|', StringSplitOptions.RemoveEmptyEntries | StringSplitOptions.TrimEntries)

No behavior change for terminals with a single executable name.

[Mingun]

It would beter to change shell.Exec type from String (?) to String[] if that possible.