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/LedgerLoad_test.cpp

@@ -36,17 +36,19 @@ class LedgerLoad_test : public beast::unit_test::suite
     struct SetupData
     {
         std::string const dbPath;
-        std::string ledgerFile{};
-        Json::Value ledger{};
-        Json::Value hashes{};
-        uint256 trapTxHash{};
+        // NOLINTBEGIN(readability-redundant-member-init)
+        std::string ledgerFile = {};
+        Json::Value ledger = {};
+        Json::Value hashes = {};
+        uint256 trapTxHash = {};
+        // NOLINTEND(readability-redundant-member-init)
     };
 
     SetupData
     setupLedger(beast::temp_dir const& td)
     {
         using namespace test::jtx;
-        SetupData retval = {td.path()};
+        SetupData retval = {.dbPath = td.path()};
 
         retval.ledgerFile = td.file("ledgerdata.json");