[feature] Provide ``is_mingw()`` recipe helper

[memsharded]

What is your suggestion?

From https://github.com/conan-io/conan/pull/12678.

The idea:

• Provide a basic helper, with return-fast strategy so it is more readable.
• It will need detailed research of non covered cases so far, like clang

Have you read the CONTRIBUTING guide?

• [ ] I've read the CONTRIBUTING guide

[mmomtchev]

Isn't it possible to implement some kind of a direct verification instead of listing the configuration cases?

[mmomtchev]

For example using the __MINGW32__ (all MinGW when 32 bits) and __MINGW64__ (only MinGW64) macros?