[gc_heap] Fix silly dict_set() template dispatch bug!

Gah this took way too long to debug!

Unrelated:

[doc] Clarify eggex doc

doc/eggex.md

@@ -287,14 +287,19 @@ performance problems.
 
 ### Flags and Translation Preferences (`;`)
 
-Flags or "regex modifiers" appear after the first semicolon:
+Flags or "regex modifiers" appear after a semicolon:
 
     / digit+ ; ignorecase /
 
-A translation preference looks like `%pref`.  It controls what regex syntax the
-eggex is translated to by default.
+A translation preference is specified with a symbol like `%pref`.  It controls
+what regex syntax the eggex is translated to by default.
 
-    / digit+ ; ignorecase %ERE /
+    / digit+ ; %ERE /                # translates to [[:digit:]]+
+    / digit+ ; %python /             # translates to \d+
+
+Flags and translation preferences together:
+
+    / digit+ ; ignorecase %python /  # translates to (?i)\d+
 
 ### Multiline Syntax
 

mycpp/gc_heap.h

@@ -1296,7 +1296,7 @@ void dict_set(Dict<K, V>* self, K key, V val) {
 
 // e.g. Dict<Str*, int>
 template <typename K, typename V>
-void dict_set(Dict<K, V*>* self, K* key, V val) {
+void dict_set(Dict<K*, V>* self, K* key, V val) {
   StackRoots _roots({&self, &key});
 
   self->reserve(self->len_ + 1);

mycpp/gc_heap_test.cc

@@ -401,27 +401,6 @@ TEST dict_test() {
 
 TEST dict_repro() {
   // For isolation
-  Str* foo = nullptr;
-  StackRoots _roots1({&foo});
-  // auto dict_si = NewDict<Str*, int>();
-  Dict<Str*, int>* dict_si = nullptr;
-  StackRoots _roots2({&dict_si});
-  dict_si = NewDict<Str*, int>();
-  log("dict_si = %p", dict_si);
-  gHeap.from_space_.AssertValid(dict_si);
-
-  Dict<int, Str*>* dict_is = nullptr;
-  log("dict_is = %p", dict_is);
-
-  StackRoots _roots3({&dict_is});
-  dict_is = NewDict<int, Str*>();
-  log("dict_is = %p", dict_is);
-  gHeap.from_space_.AssertValid(dict_is);
-
-  foo = NewStr("foo");
-
-  dict_si->set(foo, 42);           // creates slab that's not valid?
-  dict_is->set(42, kEmptyString);  // crash
 
   PASS();
 }