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/rpc/AccountObjects_test.cpp

@@ -305,9 +305,13 @@ public:
                 BEAST_EXPECT(aobjs.size() == 1);
                 auto& aobj = aobjs[0U];
                 if (i < 3)
+                {
                     BEAST_EXPECT(resp[jss::result][jss::limit] == 1);
+                }
                 else
+                {
                     BEAST_EXPECT(!resp[jss::result].isMember(jss::limit));
+                }
 
                 aobj.removeMember("PreviousTxnID");
                 aobj.removeMember("PreviousTxnLgrSeq");