Mass assert OpenDocument*() in tests

Opening a document is a prerequisite to all tests that open a document,
and success should be tested with an ASSERT instead of an EXPECT.

Done with simple search and replace with
sed -i 's/EXPECT_TRUE(OpenDocument/ASSERT_TRUE(OpenDocument/g'

Change-Id: Ia2ad22a3863b138d9222b821ddec372915c784df
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/71654
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Daniel Hosseinian <dhoss@chromium.org>

fpdfsdk/cpdfsdk_baannothandler_embeddertest.cpp

diff --git a/fpdfsdk/cpdfsdk_baannothandler_embeddertest.cpp b/fpdfsdk/cpdfsdk_baannothandler_embeddertest.cpp
index e22409f..5539056 100644
--- a/fpdfsdk/cpdfsdk_baannothandler_embeddertest.cpp
+++ b/fpdfsdk/cpdfsdk_baannothandler_embeddertest.cpp
@@ -24,7 +24,7 @@
   }
 
   void SetUpBAAnnotHandler() {
-    EXPECT_TRUE(OpenDocument("links_highlights_annots.pdf"));
+    ASSERT_TRUE(OpenDocument("links_highlights_annots.pdf"));
     m_page = LoadPage(0);
     ASSERT_TRUE(m_page);