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/libxrpl/basics/BasicConfig.cpp

@@ -55,7 +55,7 @@ Section::append(std::vector<std::string> const& lines)
                     val = "";
                     break;
                 }
-                else if (val.at(comment - 1) == '\\')
+                if (val.at(comment - 1) == '\\')
                 {
                     // we have an escaped comment char. Erase the escape char
                     // and keep looking
@@ -83,9 +83,13 @@ Section::append(std::vector<std::string> const& lines)
 
         boost::smatch match;
         if (boost::regex_match(line, match, re1))
+        {
             set(match[1], match[2]);
+        }
         else
+        {
             values_.push_back(line);
+        }
 
         lines_.push_back(std::move(line));
     }