deps.ffmpeg: Enable PDBs for FFmpeg builds on Windows

[RytoEX]

Description

Enable PDBs for FFmpeg builds on Windows if the Configuration is set to Debug or RelWithDebInfo.

Motivation and Context

Having PDBs for FFmpeg can be useful for debugging crashes. This was one of the original goals of moving the FFmpeg builds to be natively compiled.

How Has This Been Tested?

Tested locally about a year ago. Should probably be retested.

Types of changes

• Tweak (non-breaking change to improve existing functionality)

Checklist:

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