[sl4f][wlan] Partially revert "[sl4f][wlan] Remove support for WLAN through SL4F"

This partially reverts commit 2b67d5675e6411b23f2c3d344f1a3c8e62170e2e.

Reason for revert: GHP/LHP tests still rely on SL4F

Re-add only `wlan_policy`'s methods and `wlan.status` because they are
used by GHP/LHP tests.

Original change's description:
> [sl4f][wlan] Remove support for WLAN through SL4F
>
> No WLAN tests or developers use SL4F to interact with WLAN on a Fuchsia
> device.
>
> Change-Id: Ia61a8c60a963fcce6291031e5d69caeccf27476a
> Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1451210
> Reviewed-by: Ritu Gupta <guptaritu@google.com>
> Reviewed-by: Christopher Johnson <crjohns@google.com>
> Reviewed-by: Marc Khouri <mnck@google.com>
> Commit-Queue: Charles Celerier <chcl@google.com>
> Fuchsia-Auto-Submit: Charles Celerier <chcl@google.com>

Bug: 487535020
Change-Id: I97230cf4b3cf0f108f069f9c0526be804c4f6edb
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1543087
Commit-Queue: Kiet Tran <kiettran@google.com>
Reviewed-by: Charles Celerier <chcl@google.com>
Reviewed-by: Christopher Johnson <crjohns@google.com>
Fuchsia-Auto-Submit: Kiet Tran <kiettran@google.com>
Reviewed-by: Marc Khouri <mnck@google.com>
(cherry picked from commit 11a865caff0b087775a9b6a30730e4b0e048e5b4)