Everywhere: Replace single-char StringView op. arguments with chars

This prevents us from needing a sv suffix, and potentially reduces the
need to run generic code for a single character (as contains,
starts_with, ends_with etc. for a char will be just a length and
equality check).

No functional changes.

Userland/Libraries/LibCore/ArgsParser.cpp

@@ -763,7 +763,7 @@ void ArgsParser::autocomplete(FILE* file, StringView program_name, Span<char con
             continue;
         }
 
-        if (argument.starts_with("-")) {
+        if (argument.starts_with('-')) {
             option_to_complete = argument;
             completing_option = true;