RBTools had some MIME type stuff already to deal with the content types

for the API, living in rbtools.api.utils. This change takes the

generic parts of that and moves them into a new module,

rbtools.utils.mimetypes. This also adds two new methods inspired by

similar code in Review Board for guessing the MIME type of a file and

for checking to see if a MIME type matches a given accept-type pattern.
I would like to replace the file-based MIME type detection with

Google's newly open sourced magika project. At the moment, magika does

not support Python 3.12, so we have to go with this as-is.
Testing Done:

- Ran unit tests.

- Used the MIME type parsing, guessing, and matching in other changes.