Deprecate containsKey() in favor of doc["key"].is<T>()

See #2121

extras/tests/JsonObject/CMakeLists.txt

@@ -5,7 +5,6 @@
 add_executable(JsonObjectTests
 	clear.cpp
 	compare.cpp
-	containsKey.cpp
 	equals.cpp
 	isNull.cpp
 	iterator.cpp

extras/tests/JsonObject/containsKey.cpp

@@ -1,39 +0,0 @@
-// ArduinoJson - https://arduinojson.org
-// Copyright © 2014-2024, Benoit BLANCHON
-// MIT License
-
-#include <ArduinoJson.h>
-#include <catch.hpp>
-
-TEST_CASE("JsonObject::containsKey()") {
-  JsonDocument doc;
-  JsonObject obj = doc.to<JsonObject>();
-  obj["hello"] = 42;
-
-  SECTION("returns true only if key is present") {
-    REQUIRE(false == obj.containsKey("world"));
-    REQUIRE(true == obj.containsKey("hello"));
-  }
-
-  SECTION("returns false after remove()") {
-    obj.remove("hello");
-
-    REQUIRE(false == obj.containsKey("hello"));
-  }
-
-#ifdef HAS_VARIABLE_LENGTH_ARRAY
-  SECTION("key is a VLA") {
-    size_t i = 16;
-    char vla[i];
-    strcpy(vla, "hello");
-
-    REQUIRE(true == obj.containsKey(vla));
-  }
-#endif
-
-  SECTION("key is a JsonVariant") {
-    doc["key"] = "hello";
-    REQUIRE(true == obj.containsKey(obj["key"]));
-    REQUIRE(false == obj.containsKey(obj["hello"]));
-  }
-}

extras/tests/JsonObject/std_string.cpp

@@ -34,13 +34,6 @@ TEST_CASE("std::string") {
     REQUIRE("value"_s == obj["key"_s]);
   }
 
-  SECTION("containsKey()") {
-    char json[] = "{\"key\":\"value\"}";
-    deserializeJson(doc, json);
-    JsonObject obj = doc.as<JsonObject>();
-    REQUIRE(true == obj.containsKey("key"_s));
-  }
-
   SECTION("remove()") {
     JsonObject obj = doc.to<JsonObject>();
     obj["key"] = "value";