Add leading slash for path predicate if not present

This commit adds a leading slash for path predicates in both
WebFlux.fn and WebMvc.fn.

Closes gh-22795

spring-webmvc/src/main/java/org/springframework/web/servlet/function/RequestPredicates.java

@@ -107,6 +107,9 @@ public abstract class RequestPredicates {
 	 */
 	public static RequestPredicate path(String pattern) {
 		Assert.notNull(pattern, "'pattern' must not be null");
+		if (!pattern.isEmpty() && !pattern.startsWith("/")) {
+			pattern = "/" + pattern;
+		}
 		return pathPredicates(DEFAULT_PATTERN_PARSER).apply(pattern);
 	}
 

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

@@ -117,6 +117,14 @@ public class RequestPredicatesTests {
 		assertFalse(predicate.test(request));
 	}
 
+	@Test
+	public void pathNoLeadingSlash() {
+		MockHttpServletRequest servletRequest = new MockHttpServletRequest("GET", "/path");
+		ServerRequest request = new DefaultServerRequest(servletRequest, emptyList());
+		RequestPredicate predicate = RequestPredicates.path("p*");
+		assertTrue(predicate.test(request));
+	}
+
 	@Test
 	public void pathEncoded() {
 		MockHttpServletRequest servletRequest = new MockHttpServletRequest("GET", "/foo%20bar");