Rename CPDF_Document::GetPage() to GetPageDictionary().

Avoids a conflict should we wish to have the document actually
track pages, with a GetPage() that returns CPDF_Page.

Do the same thing to CPDF_DataAvail along the way.
Add some missing consts as well.

Change-Id: I2cb2213cc4c0649662fceab80407ee4a3f4cf30e
Reviewed-on: https://pdfium-review.googlesource.com/32158
Commit-Queue: dsinclair <dsinclair@chromium.org>
Reviewed-by: dsinclair <dsinclair@chromium.org>
diff --git a/fpdfsdk/cpdfsdk_interform.cpp b/fpdfsdk/cpdfsdk_interform.cpp
index 5ebf683..4f11bab 100644
--- a/fpdfsdk/cpdfsdk_interform.cpp
+++ b/fpdfsdk/cpdfsdk_interform.cpp
@@ -176,7 +176,7 @@
   ASSERT(pAnnotDict);
 
   for (int i = 0, sz = pDocument->GetPageCount(); i < sz; i++) {
-    if (CPDF_Dictionary* pPageDict = pDocument->GetPage(i)) {
+    if (CPDF_Dictionary* pPageDict = pDocument->GetPageDictionary(i)) {
       if (CPDF_Array* pAnnots = pPageDict->GetArrayFor("Annots")) {
         for (int j = 0, jsz = pAnnots->GetCount(); j < jsz; j++) {
           CPDF_Object* pDict = pAnnots->GetDirectObjectAt(j);