posix: fd_mgmt: add fd_mgmt option group

With this change, we collect implementations of functions that are
part of the POSIX_FD_MGMT Option Group into one compilation unit
(fd_mgmt.c) and provide a matching Kconfig symbol that is
reflective of the standard.

Additionally, provide Kconfig options for aliases of those functions
since Newlib-based toolchains internally use an underscore-prefixed
alias for many POSIX functions (in this case _lseek).

Prefix Zephyr-native implementations with zvfs_ to prepare for the
up-coming changes in that area.

Signed-off-by: Chris Friedt <cfriedt@tenstorrent.com>