[feature] win_bash new approach

[memsharded]

The current win_bash and run_in_windows_bash needs some improvements. This ticket would be the first iteration for improving that, to better serve the new build system integrations and for Conan 2.0.
Important points:

• It should have strictly 0 auto-detection. All information that it would need should be extracted from settings or new [conf]
• It should have a simple win_bash=True syntax, not necessary to do ugly checks in recipes about the platform. Internally, it should do nothing if not in Windows.
• It should use strictly the 2 profiles approach.
• Consider skipping using the WSL as a win_bash, as that would be a Linux environment, not a Windows one?
• tools.run_in_windows_bash() can probably be dropped if nicely supported in self.run(..., win_bash=True)
• No need to integrate it with the existing build integrations, or to be backwards compatible, it can be treated as a completely new feature to replace the previous one.

Start simple, probably just the bash wrapper itself, but not necessarily handling all the possible environment and path (cygwin, and the like) variants.

Related issue: #8883, difficult to solve without breaking...