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/app/Discrepancy_test.cpp

@@ -93,11 +93,17 @@ class Discrepancy_test : public beast::unit_test::suite
         {
             Json::Value node;
             if (an.isMember(sfCreatedNode.fieldName))
+            {
                 node = an[sfCreatedNode.fieldName];
+            }
             else if (an.isMember(sfModifiedNode.fieldName))
+            {
                 node = an[sfModifiedNode.fieldName];
+            }
             else if (an.isMember(sfDeletedNode.fieldName))
+            {
                 node = an[sfDeletedNode.fieldName];
+            }
 
             if (node && node[sfLedgerEntryType.fieldName] == jss::AccountRoot)
             {
@@ -108,11 +114,15 @@ class Discrepancy_test : public beast::unit_test::suite
                     ? node[sfFinalFields.fieldName]
                     : node[sfNewFields.fieldName];
                 if (prevFields)
+                {
                     sumPrev += beast::lexicalCastThrow<std::uint64_t>(
                         prevFields[sfBalance.fieldName].asString());
+                }
                 if (finalFields)
+                {
                     sumFinal += beast::lexicalCastThrow<std::uint64_t>(
                         finalFields[sfBalance.fieldName].asString());
+                }
             }
         }
         // the difference in balances (final and prev) should be the