Add Errorf and ErrnoErrorf

String formatting for error message can be done by using Errorf and
ErrnoErrorf. e.g. `return Errorf("{} failures", num_failure);`

The string format follows that of fmtlib, not printf.

Bug: 132145659
Test: libbase_test
Change-Id: I65f45d5f12ed23e2c14d6eb442278f467cc42e83