refactor: Add simple clang-tidy readability checks (#6556)

This change enables the following clang-tidy checks:
-  readability-avoid-nested-conditional-operator,
-  readability-avoid-return-with-void-value,
-  readability-braces-around-statements,
-  readability-const-return-type,
-  readability-container-contains,
-  readability-container-size-empty,
-  readability-else-after-return,
-  readability-make-member-function-const,
-  readability-redundant-casting,
-  readability-redundant-inline-specifier,
-  readability-redundant-member-init,
-  readability-redundant-string-init,
-  readability-reference-to-constructed-temporary,
-  readability-static-definition

src/test/jtx/impl/multisign.cpp

@@ -53,9 +53,13 @@ msig::operator()(Env& env, JTx& jt) const
 
         // The signing pub key is only required at the top level.
         if (!subField)
+        {
             sigObject[sfSigningPubKey] = "";
+        }
         else if (sigObject.isNull())
+        {
             sigObject = Json::Value(Json::objectValue);
+        }
         std::optional<STObject> st;
         try
         {
@@ -80,9 +84,13 @@ msig::operator()(Env& env, JTx& jt) const
         }
     };
     if (!subField)
+    {
         jt.mainSigners.emplace_back(callback);
+    }
     else
+    {
         jt.postSigners.emplace_back(callback);
+    }
 }
 
 }  // namespace jtx