[decompiler] rewrite set lets as just sets (#1858)

Rewrites specific kinds of lets where the return value of the `set!`
itself is meant to be used to just be `set!`s. Implemented at the let
rewrite level. Seems to work for Jak 2 so far.

Fixes #1854 .

decompiler/ObjectFile/ObjectFileDB.h

@@ -73,11 +73,12 @@ struct LetRewriteStats {
   int attack_info = 0;
   int vector_dot = 0;
   int rand_float_gen = 0;
+  int set_let = 0;
 
   int total() const {
     return dotimes + countdown + abs + abs2 + unused + ja + case_no_else + case_with_else +
            set_vector + set_vector2 + send_event + font_context_meth + proc_new + attack_info +
-           vector_dot + rand_float_gen;
+           vector_dot + rand_float_gen + set_let;
   }
 
   std::string print() const {
@@ -99,6 +100,7 @@ struct LetRewriteStats {
     out += fmt::format("  attack_info: {}\n", attack_info);
     out += fmt::format("  vector_dot: {}\n", vector_dot);
     out += fmt::format("  rand_float_gen: {}\n", rand_float_gen);
+    out += fmt::format("  set_let: {}\n", set_let);
     return out;
   }
 
@@ -120,6 +122,7 @@ struct LetRewriteStats {
     result.attack_info = attack_info + other.attack_info;
     result.vector_dot = vector_dot + other.vector_dot;
     result.rand_float_gen = rand_float_gen + other.rand_float_gen;
+    result.set_let = rand_float_gen + other.set_let;
     return result;
   }
 
@@ -140,6 +143,7 @@ struct LetRewriteStats {
     attack_info += other.attack_info;
     vector_dot += other.vector_dot;
     rand_float_gen += other.rand_float_gen;
+    set_let += other.set_let;
     return *this;
   }
 };