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_iconfit.cpp b/core/fpdfdoc/cpdf_iconfit.cpp
index a28f3bc..20ed963 100644
--- a/core/fpdfdoc/cpdf_iconfit.cpp
+++ b/core/fpdfdoc/cpdf_iconfit.cpp
@@ -20,7 +20,7 @@
   if (!m_pDict)
     return Always;
 
-  CFX_ByteString csSW = m_pDict->GetStringFor("SW", "A");
+  ByteString csSW = m_pDict->GetStringFor("SW", "A");
   if (csSW == "B")
     return Bigger;
   if (csSW == "S")