keystore: Expose @SystemApi's to wifi mainline module

Two @SystemApi's being added to allow wifi mainline module to access
formal API's:
a) KeyGenParameterSpec.Builder.setUid() to allow wifi to create/store keys
with WIFI_UID.
b) AndroidKeyStoreProvider.getKeyStoreForUid() to allow wifi to get/put
any keys stored with WIFI_UID.

Both of these API's are already permission protected in the lower
layers. There is a map of euid's stored in the native keystore which
limits which uid is allowed to access which other uid's data.

Bug: 142089671
Test: make system-api-stubs-docs-update-current-api
Change-Id: I39b92d2293bcdc26bb0a4a48a1d1e4cc0b20ad0b