liblog: logd: logcat: Split out log/logger.h into public and private.

log/logger.h pieces moved into log/log.h.  Correct for some
minor Android Coding standards.

Test: gTests liblog-unit-tests, logd-unit-tests and logcat-unit-tests
Bug: 19235719
Bug: 26552300
Bug: 31289077
Bug: 31456426
Change-Id: I0a19fd8788eec20a582e72e4c62c04534bdb1b9a