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/SHAMapStore_test.cpp

@@ -190,7 +190,7 @@ public:
             ledgers.emplace(std::make_pair(i, env.rpc("ledger", std::to_string(i))));
             BEAST_EXPECT(
                 goodLedger(env, ledgers[i], std::to_string(i), true) &&
-                getHash(ledgers[i]).length());
+                !getHash(ledgers[i]).empty());
         }
 
         ledgerCheck(env, deleteInterval + 1, 2);
@@ -229,7 +229,7 @@ public:
                 store.getLastRotated() == lastRotated || i == lastRotated + deleteInterval - 2);
             BEAST_EXPECT(
                 goodLedger(env, ledgers[i], std::to_string(i), true) &&
-                getHash(ledgers[i]).length());
+                !getHash(ledgers[i]).empty());
         }
 
         store.rendezvous();