Kernel: Refactor Filesystem-Mounts hierarchy design

[supercomputer7]

Fixes #11283.

[circl-lastname]

Shouldn't there be include guards to prevent include loops?

[supercomputer7]

Shouldn't there be include guards to prevent include loops?

There's the #pragma once statement. Still headerA.h can include headerB.h and then headerB.h can include headerA.h, which will lead to a compile error if there are class definitions in both headers that use each other.

[stale[bot]]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed in 7 days if no further activity occurs. Thank you for your contributions!

[supercomputer7]

This is not stale.