Enhance MessageHeaderAccessor support

Refine semantics of ID and TIMESTAMP headers provided to protected
MessageHeaders constructor.

Refactor internal implementation of MessageHeaderAccessor.

Support mutating headers from a single thread while a message is being
built (e.g. StompDecoder creating message + then adding session id).

Improve immutablity in NativeMessageHeaderAccessor and in
StompHeaderAccessor.

Optimize object creation for initializing messages and subsequent
accessing their headers.

Introduce MessageHeaderAccessorFactory support to enable applying a
common strategies for ID and TIMESTAMP generation to every message.

Add MessageBuilder shortcut factory method for creating messages from
payload and a full-prepared MessageHeaders instance. Also add
equivalent constructors to GenericMessage and ErrorMessage.

Issue: SPR-11468

spring-websocket/src/test/java/org/springframework/web/socket/messaging/StompSubProtocolHandlerTests.java

@@ -268,7 +268,7 @@ public class StompSubProtocolHandlerTests {
 		assertNotNull(headers.getSessionAttributes());
 		assertEquals("joe", headers.getUser().getName());
 		assertEquals("guest", headers.getLogin());
-		assertEquals("PROTECTED", headers.getPasscode());
+		assertEquals("guest", headers.getPasscode());
 		assertArrayEquals(new long[] {10000, 10000}, headers.getHeartbeat());
 		assertEquals(new HashSet<>(Arrays.asList("1.1","1.0")), headers.getAcceptVersion());