Userland: Add unveil/pledge requisites for dynamic Unicode data loading

Loading libunicodedata.so will require dlopen(), which in turn requires
mmap(). The 'prot_exec' pledge is needed for this.

Further, the .so itself must be unveiled for reading. The "real" path is
unveiled (libunicodedata.so.serenity) as the symlink (libunicodedata.so)
itself cannot be unveiled.

Userland/Applications/Assistant/main.cpp

@@ -188,7 +188,7 @@ static constexpr size_t MAX_SEARCH_RESULTS = 6;
 
 int main(int argc, char** argv)
 {
-    if (pledge("stdio recvfd sendfd rpath cpath unix proc exec thread", nullptr) < 0) {
+    if (pledge("stdio recvfd sendfd rpath cpath unix proc exec thread prot_exec", nullptr) < 0) {
         perror("pledge");
         return 1;
     }