Put HTTP_METHOD symbols in namespace

Always formally define the WebRequestMethod type, and put the
HTTP_METHOD symbols in a namespace that does not have to be included.
This allows us to avoid collisions with other web server libraries that
may define the same symbols globally.

Also we remove the includes of such colliding symbols on RP-Pico
targets.

Author: willmmiles

src/ESPAsyncWebServer.h

@@ -41,8 +41,6 @@
 #include <ESPAsyncTCP.h>
 #elif defined(TARGET_RP2040) || defined(TARGET_RP2350) || defined(PICO_RP2040) || defined(PICO_RP2350)
 #include <RPAsyncTCP.h>
-#include <HTTP_Method.h>
-#include <http_parser.h>
 #else
 #error Platform not supported
 #endif
@@ -80,11 +78,10 @@ class AsyncCallbackWebHandler;
 class AsyncResponseStream;
 class AsyncMiddlewareChain;
 
-#if defined(TARGET_RP2040) || defined(TARGET_RP2350) || defined(PICO_RP2040) || defined(PICO_RP2350)
-typedef enum http_method WebRequestMethod;
-#else
-#ifndef WEBSERVER_H
-typedef enum {
+// Namespace for web request method defines
+namespace AsyncWebRequestMethod {
+// The long name here is because we sometimes include this in the global namespace
+enum AsyncWebRequestMethodType {
   HTTP_GET = 0b0000000000000001,
   HTTP_POST = 0b0000000000000010,
   HTTP_DELETE = 0b0000000000000100,
@@ -101,8 +98,25 @@ typedef enum {
   HTTP_COPY = 0b0010000000000000,
   HTTP_RESERVED = 0b0100000000000000,
   HTTP_ANY = 0b0111111111111111,
-} WebRequestMethod;
-#endif
+};
+};  // namespace AsyncWebRequestMethod
+
+typedef AsyncWebRequestMethod::AsyncWebRequestMethodType WebRequestMethod;
+typedef uint16_t WebRequestMethodComposite;
+
+// Type-safe helper functions for composite methods
+extern inline WebRequestMethodComposite operator|(WebRequestMethodComposite l, WebRequestMethod r) {
+  return l | static_cast<WebRequestMethodComposite>(r);
+};
+extern inline WebRequestMethodComposite operator|(WebRequestMethod l, WebRequestMethod r) {
+  return static_cast<WebRequestMethodComposite>(l) | r;
+};
+
+#if !defined(ASYNCWEBSERVER_NO_GLOBAL_HTTP_METHODS) && !defined(WEBSERVER_H)
+// Import the method enum values to the global namespace
+// This will collide with some <webserver.h> values on some platforms;
+// for historical reasons they are assumed to be compatible.
+using namespace AsyncWebRequestMethod;
 #endif
 
 #ifndef HAVE_FS_FILE_OPEN_MODE
@@ -122,7 +136,6 @@ class FileOpenMode {
 #define RESPONSE_TRY_AGAIN          0xFFFFFFFF
 #define RESPONSE_STREAM_BUFFER_SIZE 1460
 
-typedef uint16_t WebRequestMethodComposite;
 typedef std::function<void(void)> ArDisconnectHandler;
 
 /*