conn: Add an helper to mark a connection as waiting for an HS descriptor

The transition for a connection to either become or go back in
AP_CONN_STATE_RENDDESC_WAIT state must make sure that the entry connection is
_not_ in the waiting for circuit list.

This commit implements the helper function
connection_ap_mark_as_waiting_for_renddesc() that removes the entry connection
from the pending list and then change its state. This code pattern is used in
many places in the code where next commit will remove this code duplication to
use this new helper function.

Part of #28669

Signed-off-by: David Goulet <dgoulet@torproject.org>

src/core/or/connection_edge.c

@@ -1354,6 +1354,21 @@ connection_ap_mark_as_non_pending_circuit(entry_connection_t *entry_conn)
   smartlist_remove(pending_entry_connections, entry_conn);
 }
 
+/** Mark <b>entry_conn</b> as waiting for a rendezvous descriptor. This
+ * function will remove the entry connection from the waiting for a circuit
+ * list (pending_entry_connections).
+ *
+ * This pattern is used across the code base because a connection in state
+ * AP_CONN_STATE_RENDDESC_WAIT must not be in the pending list. */
+void
+connection_ap_mark_as_waiting_for_renddesc(entry_connection_t *entry_conn)
+{
+  tor_assert(entry_conn);
+
+  connection_ap_mark_as_non_pending_circuit(entry_conn);
+  ENTRY_TO_CONN(entry_conn)->state = AP_CONN_STATE_RENDDESC_WAIT;
+}
+
 /* DOCDOC */
 void
 connection_ap_warn_and_unmark_if_pending_circ(entry_connection_t *entry_conn,

src/core/or/connection_edge.h

@@ -126,6 +126,9 @@ void connection_ap_mark_as_pending_circuit_(entry_connection_t *entry_conn,
 #define connection_ap_mark_as_pending_circuit(c) \
   connection_ap_mark_as_pending_circuit_((c), __FILE__, __LINE__)
 void connection_ap_mark_as_non_pending_circuit(entry_connection_t *entry_conn);
+void connection_ap_mark_as_waiting_for_renddesc(
+                                       entry_connection_t *entry_conn);
+
 #define CONNECTION_AP_EXPECT_NONPENDING(c) do {                         \
     if (ENTRY_TO_CONN(c)->state == AP_CONN_STATE_CIRCUIT_WAIT) {        \
       log_warn(LD_BUG, "At %s:%d: %p was unexpectedly in circuit_wait.", \