Label dialog constants

[kemenaran]

Dialogs used to be referenced with a raw numeric constant (like $123). Since #438, however, we can use proper constants for those dialogs (like Dialog123), which makes it easier to reference the places where a specific dialog is used in the code.

All code locations using the standard code structure were already labeled, using a call_open_dialog macro:

   ; Open dialog $123
-  ld a, $23
-  call OpenDialogInTable1
+  call_open_dialog Dialog123

However, in many places, this macro can't be used directly, because the code is conditional:

  ld e, $12 ; default dialog
  ld a, [wHasSword]
  jp nz, .swordEnd
  ld e, $13 ; dialog when Link has no sword
.swordEnd
  ld a, e
  call OpenDialogInTable0

In that case, we can still reference the dialog constant, by using the ld_dialog_low macro:

-  ld e, $12 ; default dialog
+  ld_dialog_low e, Dialog012 ; default dialog
   ld a, [wHasSword]
   jp nz, .swordEnd
-  ld e, $13 ; dialog when Link has no sword
+  ld_dialog_low e, Dialog013 ; dialog when Link has no sword
.swordEnd
   ld a, e
   call OpenDialogInTable0

We should use this macro in as many places as possible, to replace dialog raw constants by labels as much as we can.