Fix/suppress incident* google-explicit-constructor warnings

* Add explicit to conversion constructors/operators
* Remove redundant explicit of copy constructors

Bug: 28341362
Test: make with WITH_TIDY=1 DEFAULT_GLOBAL_TIDY_CHECKS=-*,google-explicit-constructor
Change-Id: I26a11bb798d25605577269ed340e97afc8566960
8 files changed