PSA: /dev/ will begin enforcing hierarchical rights

[Tamir Duberstein]

Beginning with https://fxrev.dev/771802, rights-aware operations such as fuchsia.io/Node.Clone and fuchsia.io/Openable.Open will begin enforcing hierarchical rights in /dev. This is already the behavior for all other filesystems.

Affected code which has test coverage has been updated where necessary, but please reach out if you suspect breakage resulting from this change. In most cases, fixing the problem will require you to remove fuchsia.io/OpenFlags.RIGHT_WRITABLE from fuchsia.io/Openable.Open calls, or replacing O_RDWR with O_RDONLY in open/openat calls.

[Tamir Duberstein]

In addition to the above, beginning with https://fxrev.dev/771424 /dev/ is made available as read-only in the vast majority of cases, rather than read-write as it was previously offered.

This may break components that attempt to write to /dev/null (such as interactive shells - these are still given read-write access for this reason). Please reach out if you observe regressions.