liblog: event_tag_map use unordered_map

>3 times faster access for lookup functions.  Code simplification and
C++ coding style conversion.  android_lookupEventTagNum has been
expanded to utilize the Format match, and then drops down to just
Tag match.

Performance testing on Hikey, all services stopped, shell only access,
CPU not locked had good repeatability.

$ adb reboot ; adb wait-for-device ; adb shell su root stop

Before this adjustment using binary search:

$ /data/nativetest64/liblog-benchmarks/liblog-benchmarks BM_lookupEvent*
                          iterations      ns/op
Precharge: start
Precharge: stop 231
BM_lookupEventTag           10000000        153
BM_lookupEventTag_NOT       20000000        139
BM_lookupEventFormat        10000000        153

After this adjustment strictly using std::unordered_map lookup:

$ /data/nativetest64/liblog-benchmarks/liblog-benchmarks BM_lookupEvent*
                          iterations      ns/op
Precharge: start
Precharge: stop 231
BM_lookupEventTag           50000000         56
BM_lookupEventTag_NOT      100000000         21
BM_lookupEventFormat        50000000         56

Test: gTest logd-unit-tests and liblog-unit-tests, liblog-benchmarks.
Bug: 31456426
Change-Id: I1cfc3d641c3ea9ab08d455efe0c844d3a6381440