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/ledger/Directory_test.cpp

@@ -46,14 +46,22 @@ struct Directory_test : public beast::unit_test::suite
             p->setFieldV256(sfIndexes, STVector256{});
 
             if (i + 1 == n)
+            {
                 p->setFieldU64(sfIndexNext, 0);
+            }
             else
+            {
                 p->setFieldU64(sfIndexNext, i + 1);
+            }
 
             if (i == 0)
+            {
                 p->setFieldU64(sfIndexPrevious, n - 1);
+            }
             else
+            {
                 p->setFieldU64(sfIndexPrevious, i - 1);
+            }
 
             sb.insert(p);
         }
@@ -254,8 +262,10 @@ struct Directory_test : public beast::unit_test::suite
 
         // Fill up three pages of offers
         for (int i = 0; i < 3; ++i)
+        {
             for (int j = 0; j < dirNodeMaxEntries; ++j)
                 env(offer(alice, XRP(1), USD(1)));
+        }
         env.close();
 
         // remove all the offers. Remove the middle page last