pw_base64/cmake: Migrate away from pw_auto_add_simple_module
pw_base64/cmake: Migrate away from pw_auto_add_simple_module

Migrates the CMake build rules for pw_base64 to use pw_add_library
and pw_add_test.

Change-Id: I2d83e122ffe313ffc4ef80166b591bc3fc81dece
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/119575
Pigweed-Auto-Submit: Ewout van Bekkum <638f134dbc68778d6b859fb04a64baea2b00b021@google.com>
Reviewed-by: Wyatt Hepler <cca3bedb37979eacd157a9bceb473582df8aea1e@google.com>
Commit-Queue: Auto-Submit <14637eda5603879df170705285bf30f5996692f0@pigweed.google.com.iam.gserviceaccount.com>

google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed,google/pigweed