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/TrustAndBalance_test.cpp

@@ -343,12 +343,16 @@ class TrustAndBalance_test : public beast::unit_test::suite
 
         // alice pays amazon via multiple paths
         if (with_rate)
+        {
             env(pay(alice, amazon, gw["USD"](150)),
                 sendmax(alice["USD"](200)),
                 test::jtx::path(bob),
                 test::jtx::path(carol));
+        }
         else
+        {
             env(pay(alice, amazon, gw["USD"](150)), test::jtx::path(bob), test::jtx::path(carol));
+        }
 
         if (with_rate)
         {