This function had a bug in stable (fixed in dev) when `last` returns
npos, but the function also appears to basically be duplicating what the
next split version can do, so this just removes it and uses the single
more generic split(strview, strview) method.
It was a workaround for pre-C++17 std::string which didn't support
passing a string_view to various functions/operators. There's only one
place left that needs an explicit conversion, and that's where it is
used as a map key; so just be explicit there and remove llarp::str()
everywhere else.
string_view was implicitly convertible to std::string, but
std::string_view is only explicitly convertible. This makes the
`operator std::string` explicit to be more compatible, and re-adds a
bunch of explicit string casts to the code where needed.
(This also fixes the build if changing the standard to c++17)
Adds a TrimWhiteSpace instead of using abseil's.
Adds Catch2 tests for it, and also converts the existing str tests to
catch (which look much, much nicer than the gtest ones).
