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/LibSQL/Serializer.h

@@ -163,7 +163,7 @@ private:
             bytes.append(String::formatted("{0:02x}", *(ptr + ix)));
         }
         StringBuilder bytes_builder;
-        bytes_builder.join(" ", bytes);
+        bytes_builder.join(' ', bytes);
         builder.append(bytes_builder.to_string());
         dbgln(builder.to_string());
     }