Adds support for "%v" in absl::StrFormat and related functions for string-like types (support for other builtin types will follow in future changes). Rather than specifying %s for strings, users may specify %v and have the format specifier deduced. Notably, %v does not work for `const char*` because we cannot be certain if %s or %p was intended (nor can we be certain if the `const char*` was properly null-terminated). If you have a `const char*` you know is null-terminated and would like to work with %v, please wrap it in a `string_view` before using it.

PiperOrigin-RevId: 471321055
Change-Id: Ifbb50082d301baecc7edc277975f12e7ad3ecc8a