Subtitle queue: Give more control on the queue policy when it runs late.

Let the user choose between dropping some subpics (old behavior, now the default) and blocking until the queue catches up (possibly leading to dropped frames by the video renderer).
ISR: Remove "Round up to power of two" option.

This option was meant for old GPU and it was silently disabled as soon as either the width or the height of the texture was higher than 1024.
VSFilter: Add a new config page for the new subtitle queue options.

Also increase the max number of buffered subpic to 120.
Ensure all subtitle providers are freed when closing.

Some memory was only freed when opening a new file or closing MPC-HC.
Subtitle queue: Re-enable the queue for madVR but always advise blocking.

madVR fetches the subpic when rendering not when presenting so we can always be blocking without impacting the performance too much.
Subtitle queue: Try to guess more correctly when a subpic will be needed.

The queue will attempt the minimize the number of subpics rendered.