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/protocol/STLedgerEntry.cpp

@@ -33,9 +33,11 @@ STLedgerEntry::STLedgerEntry(Keylet const& k) : STObject(sfLedgerEntry), key_(k.
     auto const format = LedgerFormats::getInstance().findByType(type_);
 
     if (format == nullptr)
+    {
         Throw<std::runtime_error>(
             "Attempt to create a SLE of unknown type " +
             std::to_string(safe_cast<std::uint16_t>(k.type)));
+    }
 
     set(format->getSOTemplate());
 
@@ -118,8 +120,10 @@ STLedgerEntry::getJson(JsonOptions options) const
     ret[jss::index] = to_string(key_);
 
     if (getType() == ltMPTOKEN_ISSUANCE)
+    {
         ret[jss::mpt_issuance_id] =
             to_string(makeMptID(getFieldU32(sfSequence), getAccountID(sfIssuer)));
+    }
 
     return ret;
 }