SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.

Migrates most of VideoCommon over to using fmt, with the exception being
the shader generator code. The shader generators are quite large and
have more corner cases to deal with in terms of conversion (shaders have
braces in them, so we need to make sure to escape them).

Because of the large amount of code that would need to be converted, the
conversion of VideoCommon will be in two parts:

- This change (which converts over the general case string formatting),
- A follow up change that will specifically deal with converting over
  the shader generators.

Ensures the destruction logic is kept local to the translation unit. It
also doesn't really do much to have it specified in the header.