[Pod] Move LogProxy interface to pod.

Does this by:
1) Moving LogProxy to log/ instead of log/table since it's not
   table-specific.
2) Moving LogProxy to pods/ instead of src/.
3) Moves the impl (LogProxyDefault) to impl/ and reduces usage of that
impl.
4) Moves the fake to tests/utils instead of multivalentTests/.

This CL is a pre-req for moving TableLogBuffer's impl to a pod.

Bug: 307607958
Flag: EXEMPT refactor
Test: build sysui, `adb shell cmd statusbar echo -b WifiTableLog:v`,
toggle wifi -> verify WifiTableLog shows up in logcat
Test: m SystemUI-application
Test: atest LogDiffsForTableTest TableLogBufferFactoryImplTest

Change-Id: Ibc06a84c03175358c3b13e9160cc7be08363e4ad