Add implicit conversion operator to std::string_view

android::base::Trim has been updated to take a std::string_view instead
of a const std::string&. Remove explicit conversions to std::string for
Trim arguments so that we do not create a unnecessary copies for the T ->
std::string conversion, only to implicitly convert from std::string ->
std::string_view immediately after.

Bug: N/A
Test: Still builds
Change-Id: Ib3db6f652f5a2b84f89cf130e3cf4a7acf9f185b