[F.Rq.] Allow saving inputs while movie is in Finished mode

Continuation of #4032 but requesting new behavior not present in any BizHawk version.

Specifically, when in Finished state, savestates should include the movie input log and inputs after up until the point of the savestate and there should probably be a way to movie and post-movie inputs as a new movie.

As far as I can tell, the current rationale for not doing this is distinguishing between savestates made before and after a movie has ended. But marking a savestate and inputs as post movie could be done without strictly throwing away inputs after a movie has ended.

Note: this is not to say necessarily we should deviate from https://tasvideos.org/LawsOfTAS/OnSavestates . There are ways to make Finished state more flexible and less of a black hole without compromising movie reliability and user safety. For savestate loading for example there could be a custom dialog when loading a savestate with inputs past the end of a movie or custom load options in the menus.

The issue names no files or tests; begin by reviewing the existing Finished-state savestate and movie-input handling, along with continuation #4032. Done requires an agreed design for preserving movie and post-movie inputs, saving them, and loading or continuing them without compromising movie reliability or user safety.