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/consensus/NegativeUNL_test.cpp

@@ -835,9 +835,13 @@ class NegativeUNLVoteInternal_test : public beast::unit_test::suite
                     for (auto const& [n, score] : *scoreTable)
                     {
                         if (n == myId)
+                        {
                             BEAST_EXPECT(score == 256);
+                        }
                         else
+                        {
                             BEAST_EXPECT(score == 0);
+                        }
                     }
                 }
 
@@ -1306,11 +1310,17 @@ class NegativeUNLVoteScoreTable_test : public beast::unit_test::suite
                         [&](std::shared_ptr<Ledger const> const& l, std::size_t idx) -> bool {
                             std::size_t k = 0;
                             if (idx < 2)
+                            {
                                 k = 0;
+                            }
                             else if (idx < 4)
+                            {
                                 k = 1;
+                            }
                             else
+                            {
                                 k = 2;
+                            }
 
                             bool add_50 = scorePattern[sp][k] == 50 && l->seq() % 2 == 0;
                             bool add_100 = scorePattern[sp][k] == 100;
@@ -1333,9 +1343,11 @@ class NegativeUNLVoteScoreTable_test : public beast::unit_test::suite
                             if (scorePattern[sp][k] == 50)
                                 return score == 256 / 2;
                             if (scorePattern[sp][k] == 100)
+                            {
                                 return score == 256;
-                            else
-                                return false;
+                            }
+
+                            return false;
                         };
                         for (; i < 2; ++i)
                         {
@@ -1753,9 +1765,11 @@ applyAndTestResult(jtx::Env& env, OpenView& view, STTx const& tx, bool pass)
 {
     auto const res = apply(env.app(), view, tx, ApplyFlags::tapNONE, env.journal);
     if (pass)
+    {
         return isTesSuccess(res.ter);
-    else
-        return res.ter == tefFAILURE || res.ter == temDISABLED;
+    }
+
+    return res.ter == tefFAILURE || res.ter == temDISABLED;
 }
 
 bool
@@ -1791,7 +1805,7 @@ VerifyPubKeyAndSeq(
             return false;
         nUnlLedgerSeq.erase(it);
     }
-    return nUnlLedgerSeq.size() == 0;
+    return nUnlLedgerSeq.empty();
 }
 
 std::size_t