feat: mark MIMEType as stable

[metcoder95]

The PR proposes to graduate MIMEType utility class from experimental to stable (or drop it completely, also a possible option).

This class was introduced in Node.js v19.1.0 and v18.13.0 as an experimental feature (circa 2 years ago). It provides a utility class for working with MIME types.

The number of issues and PRs related to this class has been minimal and the API has not suffer biggest changes since its introduction.
Most of the issues related to it has been for extensions or mere references to it.

• mimetype - 4 issues - 3 PRs
• mime type - 3 issues - 3 PRs

Its adoption can be considered as lower in range, doing a quick search of new MIMEType in GitHub, seems to throw a vast majority of results
related to the whatwg-mime userland library (util.MIMEType is also based on WHATWG MIME Type spec.).

Note: It is hard to guess the possible reasons for the low adoption of this class, but it could be due to the fact that the class is not widely known and/or due to its known limitations.

These are the few known limitations of the class:

• Performance during parsing