cameraserver: Use String8/String16 constructor conversions.

std::wstring_convert is deprecated and throws an exception, which we
can't catch (exceptions are banned). The patch replaces it with the
String8 / String16 constructors when converting from UTF-16 to
std::string.

Test: Ran fuzzers
Bug: 289467990, 289450759
Change-Id: Id956570cc85f22c81546eaf1aeb1e428c0a927a3