Pause doc: Pages drawing (#2190)

* name main fields and regs for pages drawing

* comments

* format

* more comments

* roll -> pitch (oops)

* Document `PauseContext.offsetY`, `R_PAUSE_OFFSET_VERTICAL` as "y origin 1/2"

* copypaste comment on page pitches fields

* "offset depth" -> "depth offset"

* review

src/code/z_construct.c

@@ -494,8 +494,8 @@ void Regs_InitDataImpl(void) {
     XREG(93) = 100;
     XREG(94) = 160;
     XREG(95) = 200;
-    WREG(2) = -6080;
-    WREG(3) = 9355;
+    R_PAUSE_PAGES_Y_ORIGIN_2 = -6080;
+    R_PAUSE_DEPTH_OFFSET = 9355;
     WREG(4) = 8;
     WREG(5) = 3;
     WREG(6) = 8;