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());
     }

Userland/Libraries/LibSQL/TreeNode.cpp

@@ -380,7 +380,7 @@ void TreeNode::dump_if(int flag, String&& msg)
     if (is_leaf()) {
         builder.append(", leaf"sv);
     }
-    builder.append(")");
+    builder.append(')');
     dbgln(builder.build());
 }
 

Userland/Libraries/LibSQL/TupleDescriptor.h

@@ -97,7 +97,7 @@ public:
         for (auto& element : *this) {
             elements.append(element.to_string());
         }
-        return String::formatted("[\n{}\n]", String::join("\n", elements));
+        return String::formatted("[\n{}\n]", String::join('\n', elements));
     }
 
     using Vector<TupleElementDescriptor>::operator==;

Userland/Libraries/LibSQL/Value.cpp

@@ -874,11 +874,11 @@ Vector<String> ContainerValueImpl::to_string_vector() const
 String ContainerValueImpl::to_string() const
 {
     StringBuilder builder;
-    builder.append("(");
+    builder.append('(');
     StringBuilder joined;
     joined.join(", "sv, to_string_vector());
     builder.append(joined.string_view());
-    builder.append(")");
+    builder.append(')');
     return builder.build();
 }