Fix ISR loading

- Fix ISR being auto-loaded when it shouldn't be.
- Fix ISR loading when auto-loading is disabled.
Disable some UI elements when ISR is unavailable.
Apply astyle
Prevent ISR from loading if VSFilter is already present.
Rename "Auto-load subtitles" to "Use the built-in subtitle renderer"

"Auto-load subtitles" option has been abused to disable ISR for years.
It makes more sense to change its name. Yet we still load ISR if user try to
load subtitles without any other subtitle renderer present in the graph.
ISR: Fix internal subtitle renderer when external timer is used and madVR.

Partially fixes #4141