bug#36859: Customizable fit-window-to-buffer

[Juri Linkov]

> The only practicable solution IMHO is to provide a plain
> 'vc-adjust-window-size-function' option defaulting to
> 'shrink-window-if-larger-than-buffer' and allowing 'ignore' and
> 'fit-window-to-buffer' as alternatives.

This looks like hooks.  I too like hooks, I don't understand
why vc uses such inconvenient macros as vc-run-delayed
instead of more flexible hooks.  Window management could use
hooks more often, e.g. to delay setting window-start/window-point
to later times when the buffer is ready, etc.