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/ReducedOffer_test.cpp

@@ -92,9 +92,11 @@ public:
                 // alice's offer should be fully crossed and so gone from
                 // the ledger.
                 if (!BEAST_EXPECT(!offerInLedger(env, alice, aliceOfferSeq)))
+                {
                     // If the in-ledger offer was not consumed then further
                     // results are meaningless.
                     return 1;
+                }
 
                 // bob's offer should be in the ledger, but reduced in size.
                 unsigned int badRate = 1;