avoid having to reopen terminal if the zig version has changed

[Techatrix]

Since #186, we use the GlobalEnvironmentVariableCollection to add Zig to PATH so that it is available in the integrated terminal. One limitation is that the terminal will need to be relaunched if the Zig version is being changed after the terminal has been used. To overcome this limitation, it should be possible to create a symlink to the zig executable that is added to the PATH. If a different zig executable should be used, we update the symlink instead of the PATH.