Convert string class names

Automated using git grep & sed.
Replace StringC classes with StringView classes.
Remove the CFX_ prefix and put string classes in fxcrt namespace.
Change AsStringC() to AsStringView().
Rename tests from TEST(fxcrt, *String*Foo) to TEST(*String*,
Foo).
Couple of tests needed to have their names regularlized.

BUG=pdfium:894

Change-Id: I7ca038685c8d803795f3ed02545124f7a224c83d
Reviewed-on: https://pdfium-review.googlesource.com/14151
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Ryan Harrison <rharrison@chromium.org>
diff --git a/fpdfsdk/formfiller/cffl_formfiller.cpp b/fpdfsdk/formfiller/cffl_formfiller.cpp
index fd569c7..2c6138b 100644
--- a/fpdfsdk/formfiller/cffl_formfiller.cpp
+++ b/fpdfsdk/formfiller/cffl_formfiller.cpp
@@ -233,19 +233,19 @@
   return pWnd && pWnd->OnChar(nChar, nFlags);
 }
 
-CFX_WideString CFFL_FormFiller::GetSelectedText(CPDFSDK_Annot* pAnnot) {
+WideString CFFL_FormFiller::GetSelectedText(CPDFSDK_Annot* pAnnot) {
   if (!IsValid())
-    return CFX_WideString();
+    return WideString();
 
   CPDFSDK_PageView* pPageView = GetCurPageView(true);
   ASSERT(pPageView);
 
   CPWL_Wnd* pWnd = GetPDFWindow(pPageView, false);
-  return pWnd ? pWnd->GetSelectedText() : CFX_WideString();
+  return pWnd ? pWnd->GetSelectedText() : WideString();
 }
 
 void CFFL_FormFiller::ReplaceSelection(CPDFSDK_Annot* pAnnot,
-                                       const CFX_WideString& text) {
+                                       const WideString& text) {
   if (!IsValid())
     return;