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/core/fpdfdoc/cpdf_variabletext.h b/core/fpdfdoc/cpdf_variabletext.h
index a226350..704408c 100644
--- a/core/fpdfdoc/cpdf_variabletext.h
+++ b/core/fpdfdoc/cpdf_variabletext.h
@@ -106,7 +106,7 @@
   void RearrangeAll();
   void RearrangePart(const CPVT_WordRange& PlaceRange);
   void ResetAll();
-  void SetText(const CFX_WideString& text);
+  void SetText(const WideString& text);
   CPVT_WordPlace InsertWord(const CPVT_WordPlace& place,
                             uint16_t word,
                             int32_t charset,