logd: add a SerializedLogBuffer suitable for compression

Initial commit for a SerializedLogBuffer.  The intention here is for
the serialized data to be compressed (currently using zlib) to allow
for substantially longer logs in the same memory footprint.

Test: unit tests
Change-Id: I2528e4e1ff1cf3bc91130173a107f371f04d911a
diff --git a/logd/fuzz/Android.bp b/logd/fuzz/Android.bp
index f65fbdf..9834ff0 100644
--- a/logd/fuzz/Android.bp
+++ b/logd/fuzz/Android.bp
@@ -26,6 +26,8 @@
         "liblogd",
         "libcutils",
         "libsysutils",
+        "libz",
+        "libzstd",
     ],
     cflags: ["-Werror"],
 }