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/rpc/KeyGeneration_test.cpp

@@ -164,9 +164,13 @@ public:
 
         auto const wallet = testSecretWallet(params, strings);
         if (value == strings.passphrase)
+        {
             BEAST_EXPECT(wallet[jss::warning] == strings.passphrase_warning);
+        }
         else
+        {
             BEAST_EXPECT(!wallet.isMember(jss::warning));
+        }
     }
 
     void