Replace the existing fps option by a slider

[dirkwhoffmann]

Right now, VirtualC64 allows the user to adjust the emulation speed by choosing among different fps values. Besides using the native speed which is determines by the VICII revision, values such as 30 fps or 120 fps can be selected:

Once VSYNC mode will have been ported from vAmiga, there is no need to set specific frame rates. Hence, the option can be replaced by a more general speed option which allows the user to run the emulator in a speed range from 50% - 200%. Of course, this option only takes effect if VSYNC is disabled.

Work items:

• Move the fps option from the VICII class to the C64 class.
• Replace the option (which is an enum) by a new option that represents a percentage value.
• Replace the fps field in the config panel by a slider.

The only thing I am unsure about is where to put the new option. In vAmiga, the VSYNC option is part of the Video panel:

Because the new speed option and the VSYNC option are functionally related, they should be next to each other. However, I would never search the speed option in the monitor panel.

[dirkwhoffmann]

Proposal:

• Put everything into the Monitor panel.
• Replace the VSYNC button by a Popup menu with three options: Native / Custom / VSYNC.
• If (and only if) Custom is selected, the slider is shown.

I'll implement the feature for vAmiga first to see if it works as I expect. The major use-case of this feature is to have a slowmo mode for difficult games.

[dirkwhoffmann]

Works as expected in vAmiga:

https://user-images.githubusercontent.com/12561945/209668640-61ab5c91-a501-4a35-bd52-d9bd5b15807f.mov

I'll implement it the same way for VirtualC64.

[dirkwhoffmann]

v4.6b1 is online.