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/LibWeb/CSS/Parser/Block.cpp

@@ -22,7 +22,7 @@ String Block::to_string() const
     StringBuilder builder;
 
     builder.append(m_token.bracket_string());
-    builder.join(" ", m_values);
+    builder.join(' ', m_values);
     builder.append(m_token.bracket_mirror_string());
 
     return builder.to_string();