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/basics/IntrusiveShared_test.cpp

@@ -144,7 +144,7 @@ public:
     }
 
     void
-    partialDestructor()
+    partialDestructor() const
     {
         using enum TrackedState;
 
@@ -245,7 +245,7 @@ public:
             while (!weak.empty())
             {
                 weak.resize(weak.size() - 1);
-                if (weak.size())
+                if (!weak.empty())
                     BEAST_EXPECT(TIBase::getState(id) == partiallyDeleted);
             }
             BEAST_EXPECT(TIBase::getState(id) == deleted);