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/MPToken_test.cpp

@@ -1840,11 +1840,17 @@ class MPToken_test : public beast::unit_test::suite
                 if (withAmount)
                     jv[field.fieldName] = USD(10).value().getJson(JsonOptions::none);
                 if (field == sfAsset)
+                {
                     jv[jss::Asset] = to_json(mpt.get<MPTIssue>());
+                }
                 else if (field == sfAsset2)
+                {
                     jv[jss::Asset2] = to_json(mpt.get<MPTIssue>());
+                }
                 else
+                {
                     jv[field.fieldName] = mpt.getJson(JsonOptions::none);
+                }
             };
             // All transactions with sfAmount, which don't support MPT.
             // Transactions with amount fields, which can't be MPT.