LibRegex+Everywhere: Make LibRegex more unicode-aware

This commit makes LibRegex (mostly) capable of operating on any of
the three main string views:
- StringView for raw strings
- Utf8View for utf-8 encoded strings
- Utf32View for raw unicode strings

As a result, regexps with unicode strings should be able to properly
handle utf-8 and not stop in the middle of a code point.
A future commit will update LibJS to use the correct type of string
depending on the flags.

Userland/Libraries/LibDebug/DebugSession.cpp

@@ -422,7 +422,7 @@ void DebugSession::update_loaded_libs()
         auto rc = re.search(vm_name, result);
         if (!rc)
             return {};
-        auto lib_name = result.capture_group_matches.at(0).at(0).view.u8view().to_string();
+        auto lib_name = result.capture_group_matches.at(0).at(0).view.string_view().to_string();
         if (lib_name.starts_with("/"))
             return lib_name;
         return String::formatted("/usr/lib/{}", lib_name);