Add fallback for getting device path.

[dcnieho]

Description

For various software devices i have, the devicePath remains empty upon DShow::Device::EnumVideoDevices(). I have implemented a fallback method for getting the devicepath.

Motivation and Context

I'd like to have device paths for as many devices, software or hardware, as possible.

How Has This Been Tested?

I have run enumDevices, called from my own application, and devicePaths for software devices are now created.
DShow::Device.SetVideoConfig() also works fine for a software device with this now non-empty path.

Types of changes

Unclear to me, seems to be a new feature.

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[WizardCM]

Are there specific devices where you ran into issues that we could verify with?

[dcnieho]

I have observed this with two devices, both https://obsproject.com/forum/resources/obs-virtualcam.949/, and the directshow adapter for Basler machine vision cameras (part of their Pylon runtime)--the latter you can't test without having a Basler camera i think. These are both software devices i guess.

[dcnieho]

Ping on this one. Its also how ffmpeg's dshow gets their device paths

[dcnieho]

And sorry to canabalize this PR, but i can't post issues to this repo. Is it being considered to re-apply 8f2ef91? I would love to have this functionality. Anything i can do to help?