liblog: logcat: logprint support -v descriptive

Expand logprint feature to pull out the log tag description
fields, parse them and merge into the logging content.  Add
-v descriptive, -v colour(british, hidden) and -v help. Also
added a unit test for the descriptive format borrowing from
event tags that have been unchanged since 2009.

Had to add -v help because we have too many undocumented
formats and format adverbs.

Test: gTest logcat-unit-tests --gtest_filter=logcat.descriptive
Bug: 31456426
Change-Id: I93a1c003b7a3f4c332544946fdedb7277919cec3