Reduce method visibility when possible

Reduce method visibility for package private classes when possible.

In the case of abstract classes that will eventually be made public,
the class has been made public and a package-private constructor has
been added.

Issue gh-8945

web/src/test/java/org/springframework/security/web/authentication/DefaultLoginPageGeneratingFilterTests.java

@@ -214,7 +214,7 @@ public class DefaultLoginPageGeneratingFilterTests {
 			return null;
 		}
 
-		public String getClaimedIdentityFieldName() {
+		String getClaimedIdentityFieldName() {
 			return "unused";
 		}
 

web/src/test/java/org/springframework/security/web/context/request/async/WebAsyncManagerIntegrationFilterTests.java

@@ -137,7 +137,7 @@ public class WebAsyncManagerIntegrationFilterTests {
 			return this.t;
 		}
 
-		public void join() throws InterruptedException {
+		void join() throws InterruptedException {
 			this.t.join();
 		}
 

web/src/test/java/org/springframework/security/web/csrf/CsrfFilterTests.java

@@ -394,7 +394,7 @@ public class CsrfFilterTests {
 			super(actual, CsrfTokenAssert.class);
 		}
 
-		public CsrfTokenAssert isEqualTo(CsrfToken expected) {
+		CsrfTokenAssert isEqualTo(CsrfToken expected) {
 			assertThat(this.actual.getHeaderName()).isEqualTo(expected.getHeaderName());
 			assertThat(this.actual.getParameterName()).isEqualTo(expected.getParameterName());
 			assertThat(this.actual.getToken()).isEqualTo(expected.getToken());