Deprecate pathExtension routing predicates

Closes gh-34103

spring-webmvc/src/test/java/org/springframework/web/servlet/function/RequestPredicatesTests.java

@@ -223,6 +223,7 @@ class RequestPredicatesTests {
 		assertThat(predicate.test(request)).isFalse();
 	}
 
+	@SuppressWarnings("removal")
 	@Test
 	void pathExtension() {
 		RequestPredicate predicate = RequestPredicates.pathExtension("txt");
@@ -237,6 +238,7 @@ class RequestPredicatesTests {
 		assertThat(predicate.test(initRequest("GET", "/file"))).isFalse();
 	}
 
+	@SuppressWarnings("removal")
 	@Test
 	void pathExtensionPredicate() {
 		List<String> extensions = List.of("foo", "bar");

spring-webmvc/src/test/java/org/springframework/web/servlet/function/ToStringVisitorTests.java

@@ -29,7 +29,6 @@ import static org.springframework.web.servlet.function.RequestPredicates.method;
 import static org.springframework.web.servlet.function.RequestPredicates.methods;
 import static org.springframework.web.servlet.function.RequestPredicates.param;
 import static org.springframework.web.servlet.function.RequestPredicates.path;
-import static org.springframework.web.servlet.function.RequestPredicates.pathExtension;
 import static org.springframework.web.servlet.function.RouterFunctions.route;
 
 /**
@@ -61,6 +60,7 @@ class ToStringVisitorTests {
 		assertThat(result).isEqualTo(expected);
 	}
 
+	@SuppressWarnings("removal")
 	@Test
 	void predicates() {
 		testPredicate(methods(HttpMethod.GET), "GET");
@@ -68,8 +68,6 @@ class ToStringVisitorTests {
 
 		testPredicate(path("/foo"), "/foo");
 
-		testPredicate(pathExtension("foo"), "*.foo");
-
 		testPredicate(contentType(MediaType.APPLICATION_JSON), "Content-Type: application/json");
 
 		ToStringVisitor visitor = new ToStringVisitor();

spring-webmvc/src/test/kotlin/org/springframework/web/servlet/function/RouterFunctionDslTests.kt

@@ -192,6 +192,7 @@ class RouterFunctionDslTests {
 				null
 			}
 		}
+		@Suppress("DEPRECATION")
 		GET(pathExtension { it == "properties" }) {
 			ok().body("foo=bar")
 		}