Disable Capture device: dropdown when Capture method: is not Video Capture Device

[Toufool]

Self explanatory. I think this will avoid confusion. When it's disabled, maybe we can set the text to something like "Select video capture device above" or something. Kind of like this

And then when Video Capture Device is selected, we can enable the dropdown to select the device.

[Avasam]

I generally agree with the request for a design change here. But there's one critical issue the current design works around:
If a video device would cause extra lag(1) or cause an unrecoverable error(2) and is the default(3) then the "Video Capture Device" option becomes unusable.

---

1. Shouldn't be much of an issue with async device info. Was more of a problem during development. Could maybe cause the GV-USB2 to freeze?
2. Unfortunately OBS' own integrated Virtual Cam is such a case that causes an uncatchable hard crash with OpenCV.
3. I think it's better if there's a way for the user to select the capture device they wanna use before we try to use it.

We could unselect the capture device whenever a different capture method is selected. I doubt a regular user would often swap between them and need the capture device to be remembered. Then your request can be implemented as-is.

[Toufool]

Functionality for this looks good.