Remove the OS_VolumeTable definition from all BSPs, but provide
a default (empty) one to support linking when OMIT_DEPRECATED is
not set.

Do not assume BSP volume table provides a "/cf" directory map.
Instead, create a UT-specific map of a consistent name, and use
that.

Add a distinct type for FS_BASED entries, and an UNKNOWN value
for when a type is actually not yet identified.

This can be used to identify the FS type first at the shared
layer, then in the implementation layer as a fallback option
if not identifiable in the shared layer.

Use the volume name prefix "RAM" as a hint that the volume
is supposed to be a VOLATILE disk as opposed to a normal disk.
This is done in shared layer so it applies to all OS types.

Confirm that the "selectable" flag is set before
calling the underlying select() API.

Also update unit tests to match.