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/xrpld/app/main/NodeIdentity.cpp

@@ -12,7 +12,7 @@ getNodeIdentity(Application& app, boost::program_options::variables_map const& c
 {
     std::optional<Seed> seed;
 
-    if (cmdline.count("nodeid"))
+    if (cmdline.contains("nodeid"))
     {
         seed = parseGenericSeed(cmdline["nodeid"].as<std::string>(), false);
 
@@ -37,7 +37,7 @@ getNodeIdentity(Application& app, boost::program_options::variables_map const& c
 
     auto db = app.getWalletDB().checkoutDb();
 
-    if (cmdline.count("newnodeid") != 0)
+    if (cmdline.contains("newnodeid"))
         clearNodeIdentity(*db);
 
     return getNodeIdentity(*db);