rtsp: refactor method handling and improve error checks

- convert the method switch() to a simple table

- avoid converting the methods from external to internal numbers, they were
  the same anyway so keep the external ones, just use the old defines.

- fix range check. It wrongly used the method numbers as bitmask, which made
  the check not work previously. Also error on OOM.

- Dropped the session-id check. It too wrongly did a bitmask check which was
  wrong and never worked. When fixed, it broke test cases so I dropped the
  entire check.

- split out rtsp_setup_request() from rtsp_do()

- replace the httpversion variable with a define

Closes #22505

lib/rtsp.h

@@ -30,4 +30,18 @@ extern const struct Curl_protocol Curl_protocol_rtsp;
 #define Curl_rtsp_parseheader(x, y) CURLE_NOT_BUILT_IN
 #endif
 
+#define RTSPREQ_NONE CURL_RTSPREQ_NONE
+#define RTSPREQ_OPTIONS CURL_RTSPREQ_OPTIONS
+#define RTSPREQ_DESCRIBE CURL_RTSPREQ_DESCRIBE
+#define RTSPREQ_ANNOUNCE CURL_RTSPREQ_ANNOUNCE
+#define RTSPREQ_SETUP CURL_RTSPREQ_SETUP
+#define RTSPREQ_PLAY CURL_RTSPREQ_PLAY
+#define RTSPREQ_PAUSE CURL_RTSPREQ_PAUSE
+#define RTSPREQ_TEARDOWN CURL_RTSPREQ_TEARDOWN
+#define RTSPREQ_GET_PARAMETER CURL_RTSPREQ_GET_PARAMETER
+#define RTSPREQ_SET_PARAMETER CURL_RTSPREQ_SET_PARAMETER
+#define RTSPREQ_RECORD CURL_RTSPREQ_RECORD
+#define RTSPREQ_RECEIVE CURL_RTSPREQ_RECEIVE
+#define RTSPREQ_LAST CURL_RTSPREQ_LAST
+
 #endif /* HEADER_CURL_RTSP_H */