ob_tran.cpp: setup(): fix quadratic performance issue in the number of projection parameters

Does not matter for nominal use cases, but fixes huge processing time
on fuzzer generated PROJ strings with huge number of parameters.

Fixes https://issues.oss-fuzz.com/issues/499119740

Author: rouault

src/projections/ob_tran.cpp

@@ -1,6 +1,7 @@
 
 #include <errno.h>
 #include <math.h>
+#include <set>
 #include <stddef.h>
 #include <string.h>
 
@@ -206,15 +207,18 @@ PJ *PJ_PROJECTION(ob_tran) {
         return destructor(P, PROJ_ERR_INVALID_OP_ILLEGAL_ARG_VALUE);
     }
 
+    // Colect used parameters from the R object
+    std::set<std::string> setUsedRParams;
+    for (auto r = R->params; r; r = r->next) {
+        if (r->used) {
+            setUsedRParams.insert(r->param);
+        }
+    }
+
     // Transfer the used flag from the R object to the P object
     for (auto p = P->params; p; p = p->next) {
-        if (!p->used) {
-            for (auto r = R->params; r; r = r->next) {
-                if (r->used && strcmp(r->param, p->param) == 0) {
-                    p->used = 1;
-                    break;
-                }
-            }
+        if (!p->used && setUsedRParams.find(p->param) != setUsedRParams.end()) {
+            p->used = 1;
         }
     }