hidl_string no longer will provide an implicit cast to const char* as it
interfers with other expected behaviors of the class. It now emulated
std::string in requiring a call to .c_str() to get the same behavior.
Bug: 36532780
Test: Build the tree
Change-Id: I2ce4354619a99d7c5ae8b39762d5506891ccd1ed
cfcdceaa4f